man, thats alot!, heres my spec i spent £600 on it,

pentium 4 3ghz
1 gig ddr ram
120gig hdd
19'' monitor
ati radeon 9800xt 256mb

sound network card extra fan cd rw +a dvd rom.

with your extra £500 you could get a might lot! thats twice my pc nearly!!! (this is if you build it yourself, i built mine on my own) if you buy one froma shop you most likely be ripped off and probably get one not as good as mine. if i were you id build it yourself or ask a friend or something. www.ebuyer.com are ok but sometimes unreliable. there are lots of sites out there that sell pc parts, if u want a list of sites just ask.