buy a funky lan party motherboard, and slap a nice 3200xp in there, £230
ati 9800 should do at £125
with some drives, 2 samsung spin points for £100, 2x80gig SATA, with RAID
a good case from coolermaster is not cheap but will last you and you can get one with loads of drive bays just in case,
a cd/ dvd re-writer will set you back about £50
and a silent pure power psu from thermaltake at £60 for a good peice of 450W!!
= £775 i think then whatever else you need spend a bit more on, easy peasy, look at all the choises