This would be better, better mobo for clocking and much better gfx card:
CP-152-AM AMD Athlon 64 X2 Dual Core 3800+ (Socket 939) - OEM (CP-152-AM)
£169.95 £169.95
FG-000-AR Arctic Cooling Freezer 64 Pro CPU Cooler (Socket 754/939/940) (FG-000-AR)
£15.95 £15.95
MB-046-MS MSI K8N Neo4 Platinum nForce4 Ultra (Socket 939) PCI-Express Motherboard (MB-046-MS)
£64.95 £64.95
MY-046-GL GeIL 2GB (2x1GB) PC3200 Value Dual Channel Kit CAS3 (GE2GB3200BDC) (MY-046-GL)
£94.95 £94.95
GX-048-PC PowerColor ATI Radeon X1800 XT 512MB GDDR3 AVIVO TV-Out/Dual DVI (PCI-Express) - Retail (GX-048-PC)
£194.95 £194.95
HD-001-HI Hitachi Deskstar T7K250 NCQ 160GB SATA-II 8MB Cache - OEM (0A31637) (HD-001-HI)
£44.95 £44.95
CA-040-AN Antec Sonata II Piano Black Quiet Case - 450W Smart Power PSU (CA-040-AN)
£65.95 £65.95
Subtotal £651.65
VAT £114.04
Total £765.69
If you wanted you could up the spec of the gfx card, or maybe some better CAS2 ram for the spare £35