Yeah... if you're gonna go with brands, Dell and Alienware are both good. I rteccomend custom-building, just lets you have more options, plus, if you do it yourself, you save money on labour...
I've always been an Intel person myself, so I'd reccomend a 2.8 Ghz or better processor, with HT of course...
Corsair RAM is awesome...
ATI 9600 Pro or XT willl do the trick for 99.9% of today's games, if you want to be prepared for the future, get a 9800 XT/ Pro...
ASUS Motherboards are good for custom-building and o/cing...
WesternDigital HardDrives are awesome...
WinXP is probalby the best Windows out there ATM, 2K isn't bad either though...
For sound, I'd reccomend and Audigy 2ZS sound card, and if you're going with speakers Creative's are good in the lower price range, if youve got mopney to burn, Klipsch is awesome...
I think that just about covers it...