I think the most common mistake computer buyers make is that they buy computers based on what they believe they need now; that's off-the-mark on two accounts: (1) Unanticipated needs, and (2) Future needs. So what often happens is that buyers end up (1) Disappointed by how much they find out they want to do that they either cannot do or cannot do with adequate performance, and (2) Disappointed by how quickly they find their computer becomes obsolute, unable to run the software and do the things that they end up wanting it to do next year, the year after, etc.
If you're buying a computer to use for the next year, then you probably cannot go that far off-target. If, instead, you're looking to purchase a laptop to use for the next few years, then you really want to think long and hard, look as far ahead as you can, make your guesses very liberal, figuring you'll end up wanting to do a lot of things that perhaps right now you don't think you'll end up wanting to do.
For me, right now, a typical multimedia laptop should have the following minimal specs:
Dual-core, 1.83 or 2 GHz processor
Microsoft Windows Media Center Edition (not just "Home Edition")
17" wide-screen XGA, or better yet XGA+ or SXGA or UXGA -- the better the video, the better the video, eh?
2GB RAM memory
100GB Hard Disk; 200GB would be better -- you may be thinking photos and such now, but in a year or so you may be thinking video
DVD burner -- same reason
