Here is a Phenom II build then:
Phenom II 940 3ghz ~ £180 to £190
Phenom II 920 2.8ghz ~ £155 to £165
790GX motherboard ~ £80 to £100
780G motherboard ~£60 to £75
4gb DDR2 ~ £40 to £50
500GB HDD ~£45
HD4850 graphics card ~ £120
HD4830 graphics card ~ £90
Xigmatek 650W modular PSU ~ £60
Antec 300 ~ £40 to £50
DVD writer ~ £15
Vista or XP disc ~ £70+
22" Samsung LCD ~£140
Logitech keyboard and mouse ~£20
So for around £800 to £900 you can do a complete build which should last a while!!
I have an Athlon XP processor which I still use in a server at home and it is still plodding along over 5 years later!! My old ATI 9500pro graphic card which is over 5 years old is still working in a colleague's computer too!!