Desktop replacement laptops are ideal if you don't have space for a full-size desktop PC, but still need to do your number crunching. With powerful components, a desktop replacement can rival a full-sizer's performance. The advantage, of course, is that when you've finished using it at the end of the day, you can close the lid and hide it away.
For the best in performance, Intel's latest batch of processors -- codenamed Penryn -- are the best. These are made using a smaller processor core than their predecessors -- using 45nm technology rather than 65nm -- which means they can run faster without generating as much heat. They also draw less power. Penryn is just the codename -- they're all Core 2 Duo chips. Only four suitable for laptops have been released so far, so the ones to look out for are T9500, T9300, T8300 and T8100.
Keep in mind that Windows Vista requires a decent amount of RAM if you want it to run smoothly. At the bare minimum, you should look for 2GB of RAM, although the more, the better.
If your aim is to game, then you'll need a laptop with a dedicated graphics chip from the likes of ATI or Nvidia. Some machines can even use two chips in tandem, such as the Nvidia GeForce 8600 GT SLI. While you won't get double the performance of a single chip, there's still a large benefit.
A 17-inch display will provide plenty of desktop space for working. For viewing HD content, you'll need a screen with a resolution of 1,920x1,080 pixels to enjoy 1080p footage at its best. Consider, too, that if this does actually replace your desktop, you'll probably need at least 250GB of storage for all your files. Happily, some machines come with twice that amount.
Finally, while they might look portable, most of these desktop replacements are hefty. You won't get more than a couple of hours of battery life. They're really designed to be used in one place rather than taken on the road.