400 bucks? with my 400 bucks I got the mobo, ram and cpu on my signature.. from newegg.. your radeon is good enough.. all you need is a new sound card and you can hand down the crappy dell..
I would say, add $20-50 for a case (really nice ones in newegg) and $50-70 for a sound card, all together 500'ish bucks you just went from crap to good.
_P4 Northwood 2.8C Ghz HT
_Kingston 512 DDR400 Ram [2x 256]
_Awesome looking white plain case with cool green and red power/HD lights, and a newely acquired Intel P4 sticker!