I thought I'd spec out the best Core 2 Duo system I could for under £600. As a "budget" gaming machine this should be pretty damn good. For another £45 you can upgrade the graphics to an x1800xt. Or if gaming isn't your thing then swapping out the 7600GT for a lower end model will give you enough money to get a Duo 6600.
MB-011-IN Intel DP965LT 965 (Socket 775) PCI-Express DDR2 Motherboard (MB-011-IN)
£74.95 £74.95
CP-126-IN Intel Core 2 DUO E6300 "LGA775 Conroe" 1.86GHz (1066FSB) - Retail (CP-126-IN)
£129.95 £129.95
MY-012-GS G.Skill 2GB DDR2 LA PC2-5300 (2x1GB) CAS4 Dual Channel Kit (F2-5400PHU2-2GBLA) (MY-012-GS)
£99.95 £99.95
GX-025-BG BFG 3DFuzion GeForce 7600 GT 256MB GDDR3 TV-Out/DVI (PCI-Express) - Retail (GX-025-BG)
£99.95 £99.95
CA-052-AN Antec NSK4400 Mini Tower Case - 380W SmartPower PSU (CA-052-AN)
£34.95 £34.95
HD-018-SA Samsung SpinPoint P SP2504C 250GB SATA-II 8MB Cache - OEM (HD-018-SA)
£43.50 £43.50
CD-059-LO Liteon DRW-6S160P-05C 16x16 DVD±RW Dual Layer ReWriter (Black) - OEM (CD-059-LO)
£18.25 £18.25
Subtotal £501.50
VAT £87.77
Total £589.27
MB-011-IN Intel DP965LT 965 (Socket 775) PCI-Express DDR2 Motherboard (MB-011-IN)
£74.95 £74.95
CP-126-IN Intel Core 2 DUO E6300 "LGA775 Conroe" 1.86GHz (1066FSB) - Retail (CP-126-IN)
£129.95 £129.95
MY-012-GS G.Skill 2GB DDR2 LA PC2-5300 (2x1GB) CAS4 Dual Channel Kit (F2-5400PHU2-2GBLA) (MY-012-GS)
£99.95 £99.95
GX-025-BG BFG 3DFuzion GeForce 7600 GT 256MB GDDR3 TV-Out/DVI (PCI-Express) - Retail (GX-025-BG)
£99.95 £99.95
CA-052-AN Antec NSK4400 Mini Tower Case - 380W SmartPower PSU (CA-052-AN)
£34.95 £34.95
HD-018-SA Samsung SpinPoint P SP2504C 250GB SATA-II 8MB Cache - OEM (HD-018-SA)
£43.50 £43.50
CD-059-LO Liteon DRW-6S160P-05C 16x16 DVD±RW Dual Layer ReWriter (Black) - OEM (CD-059-LO)
£18.25 £18.25
Subtotal £501.50
VAT £87.77
Total £589.27