Built mine.
P4, 2 100gig 7200 rpm HD's, a gig'o ram, dual monitors, 75 gig External firewire HD back-up, CDRW I think the processor is 1.8 or 2.1 GHz, ASUSP4 mobo, RME 96/52 sound card, Win XP Pro, Total dedicated DAW, ROCK Solid!
Building your own is the only way to go. It's going to cost you a lot more than the $699 DELL Special, but you'll end up with a WAY better machine.
It's not difficult to do, if you understand what components make up a PC; just read the directions where you need to and put it together.
Your O/S and your recording software is all you should have on it, save and except of course the necessary drivers. Retail PC's come loaded with so much crap on them that they are practically rendered useless for serious recording work.