Im assuming you have monitor, keyboard, etc....
DFI Lanparty Ultra-D
G. Skill 2*1gb extreme series RAM
OCZ powerstrem 520W
Seagate 250gb SATA hdd
Zalman 9500 (or big typhoon, scythe ninja, w/e)
a case you like, dvd burner
I dont know how much this adds up to because i dont know the prices in pounds.