AMD Athlon 64 3700+ San Diego 90nm (Socket 939) - Retail (ADA3700BNBOX) (CP-121-AM)
£147.99
Asus A8N-E nForce4 Ultra (Socket 939) PCI-Express Motherboard (MB-088-AS)
£72.79
GeIL 1GB (2x512MB) PC3200 Value Dual Channel Kit CAS2.5 (GE1GB3200BHDC) (MY-005-GL)
£64.57
Sapphire ATI Radeon X1800 XT 256MB GDDR3 AVIVO TV-Out/Dual DVI (PCI-Express) - Retail (GX-121-SP)
**this week only**
£217.32
Total inc VAT: £502.67
OR
AMD Athlon 64 X2 Dual Core 3800+ (Socket 939) - OEM (CP-152-AM)
£193.82
Asus A8N-E nForce4 Ultra (Socket 939) PCI-Express Motherboard (MB-088-AS)
£72.79
GeIL 1GB (2x512MB) PC3200 Value Dual Channel Kit CAS2.5 (GE1GB3200BHDC) (MY-005-GL)
£64.57
PowerColor ATI Radeon X850 XT 256MB GDDR3 TV-Out/DVI (PCI-Express) - Retail (GX-037-PC)
£152.69
Arctic Cooling Freezer 64 Pro CPU Cooler (Socket 754/939/940) (FG-000-AR)
£15.22
Total inc VAT: £499.09
I presume you have a decent power supply?