Choosing a computer and where to buy it are decisions so intertwined that we’ve combined them for this special guide.

We describe the newest developments in the world of desktops and laptops (available to subscribers), complete with our latest Ratings, that could affect your choice of a computer. That’s followed by our exclusive Ratings of online and brick-and-mortar computer retailers, which can point you to the best place to buy the machine you want. First, the news and what it means for you:

If you’re looking for a bargain, now is a good time to buy. Prices for both desktops and laptops have continued to decline. More than 70 percent of all desktops currently sell for less than $1,000, and more than 75 percent of laptops for under $1,500, according to Synovate, a market research company.

Prices on more rudimentary computers are looking even better. You can buy a basic, bare-bones desktop without a monitor from Compaq or HP for about $300, and laptops from Compaq and Dell now cost as little as $500.

The launch of Intel’s Core 2 Duo processors is creating great deals on older Pentium-based dual-core desktops. Prices on AMD desktops using lower-end Athlon 64 X2 chips have also dropped. Dual-core systems provide potentially better performance than those with single processors. You can now get a desktop with a dual-core chip for as little as $650. In spring 2006 a similar computer would have cost you about $840. Although Intel was expected to ship one million Core 2 Duo chips within seven weeks of their introduction in August 2006, many computer makers plan to keep Pentium-based systems around for a while.

For the best desktop values, look to single-processor systems with Intel Celeron or AMD Sempron processors or to dual-processor models with Pentium D or Athlon 64 X2 chips. Those systems should be speedy enough for most users.

However, if you are a serious gamer or like to do video editing, design work, or 3D graphics, you may want to step up to a model with the new Intel Core 2 Duo processor. In our tests, the Core 2 Duo for desktops was about 30 percent faster than the Pentium D and competitor AMD’s Athlon 64 X2. The Core 2 Duo also used 25 percent less power than the Pentium D, and 12 percent less than the Athlon 64 X2. As a result, it generated less heat.

The Core 2 Duo for laptops did not arrive in stores in time for testing. We tested two laptops with AMD’s dual-core processor. The HP Pavilion dv2000z and dv6000z both have the Turion 64 X2 TL-52 processor. The systems showed only marginal speed improvements over their single-processor counterparts, and they cost about $100 more.

Both Microsoft and Apple have major revamps of their operating systems on the way. Microsoft Windows Vista, due in January 2007, will have a new interface and enhanced security. Most systems currently on sale are Windows Vista Capable, meaning they have the minimum specs to support the new operating system. Although Microsoft says 512 megabytes of RAM is enough to run a minimal version of Vista, we recommend getting at least 1 gigabyte.

Systems called Windows Vista Premium Ready are able to run Vista’s Aero interface. It is primarily a desktop face-lift that also includes some usability tweaks. An even higher-end Vista interface, Aero Glass, will also be available on some PC models.

Apple recently released details on some of the features of the next version of OS X, which is due in the spring. These include Time Machine, an automated backup program, and Spaces, a feature that allows you to have several desktops open on your screen at once.

The final version of Boot Camp, which lets you run Windows XP on the Mac, will also be packaged with the new operating system. You’ll have to buy your own copy of Windows XP, however.

If you plan to buy a computer now but would prefer its forthcoming operating system, ask the manufacturer whether it intends to issue upgrade coupons, which would save you some money when the new system becomes available.

Desktops and laptops are starting to ship with high-definition DVD players, but we don’t recommend those systems yet. The high-definition playback on the laptops we tested was not ready for prime time, with so-so video and tiny text on Web pages because of the systems’ high resolution. As for desktops, they require HDCP-compliant monitors and video cards for content protection, which are not yet very common. If your system lacks those components, you won’t be able to view high-definition Hollywood content. Finally, the battle over which high-def format--Sony’s Blu-ray or Toshiba’s HD DVD--will become dominant is far from over, so you could end up with an obsolete player.

Web-based retailers tended to score better overall on price in the latest Computer Shopping Survey, conducted by the Consumer Reports National Research Center.  Amazon.com was the only vendor to get the highest rating for its prices in the survey, while PC/Mac Connection.com, PC/Mac Mall.com, and TigerDirect.com all rated better than average and were standouts for selection. Bear in mind, however, that most independent online retailers sell both new and refurbished systems, so make sure you know which you’re getting.

One limitation of independent online retailers is that you may not have a lot of flexibility in customizing. The best place to do that is at the manufacturer’s own site. Among those, Apple rated tops in our survey, with superior selection and service. Lenovo (IBM) ranked among the highest overall for Windows PCs, though Dell earned top marks for selection.

Our respondents were less satisfied overall with their buying experiences at retail stores. Most offered average prices at best and few earned high marks for their service or selection. Two exceptions were Apple’s retail stores and Micro Center, both of which were highly rated for selection and service.

For retailers with both online and brick-and-mortar stores, our survey respondents fared better by going the Web route. Costco and Circuit City’s Web sites, for example, offered slightly better selection than their traditional stores, our respondents told us. One advantage of dealing with a retailer that has both: You can buy the system online, then pick it up almost immediately from the store (as did 61 percent of our respondents who bought computers on Circuit City’s Web site). If you’re dissatisfied with your computer, you can also return it to the store rather than having to ship it.

Some manufacturers are cutting back their rebate programs. Sony, for example, has already shrunk the percentage of Vaio systems with mail-in rebate offers from 20 percent to 5 percent. Dell announced plans to reduce the rebates and promotions on all its product lines by 70 percent within the next 12 to 18 months.

That’s fine by us. The decline of rebates doesn’t mean that prices will rise. Plus, the complexity and variety of special offers have made it difficult to know exactly what you can get for your money, with deals changing daily and sometimes more often. Now it should be easier to recognize a good price when you see one.

For a budget desktop or laptop, 512MB of RAM should be sufficient unless you’re planning to run any version of Vista. In that case, get 1GB of RAM. Workhorse desktops and laptops require enough power to run video editing, 3D games, and other intensive applications, so plan on 1GB of RAM.

A budget desktop should cost about $500 without a monitor and under $800 with a 17-inch LCD. It should have a 160GB hard drive, integrated video, and a DVD burner. Workhorse users will spend about $1,500 for a desktop with a 250GB hard drive, 256MB of dedicated video RAM, a DVD burner and a DVD-ROM drive, and a 19-inch monitor.

Less than $1,000 will get you a budget laptop with a 60GB hard drive, a CD-RW/DVD combo drive, integrated video, and a 14.1- or 15.4-inch screen. Laptops in this category generally weigh 5 to 7 pounds. For a laptop that can serve as a desktop replacement, get an 80GB hard drive, a DVD-RW drive, and 128MB of dedicated video RAM. You’ll want a 14.1- to 15.4-inch widescreen display for portable use or a 17-inch one for desktop use. These systems are hefty, at 5 to 10 pounds, and will cost you $1,000 to $3,000.

For a system you can easily tote, try a slim-and-light laptop with 512MB of RAM, a 60GB hard drive, a CD-RW/DVD combo drive, integrated video, and a carry weight of less than 5 pounds. You can get it for $1,000 to $2,000.