AMD Athlon 64 3500+ Venice 90nm (Socket 939) - Retail (ADA3500BPBOX) (CP-119-AM)
£139.77
Gigabyte K8NMF-9 nForce4 Micro ATX (Socket 939) PCI-Express Motherboard (MB-041-GI)
£49.29
Corsair 1GB DDR Value Select PC3200 CAS3.0 Kit (2x512MB) (VS1GBKIT400C3) (MY-061-CS)
£56.34
Seagate Barracuda 7200.9 NCQ 80GB ST3808110AS SATA-II 8MB Cache - OEM (HD-051-SE)
£36.37
Antec SLK3800BUK Black Quiet Midi Tower Case - 400W SmartPower PSU (CA-048-AN)
£61.04
Samsung SH-W162C 16x16 DVD±RW Dual Layer ReWriter (Black) (CD-068-SA)
£23.44
PowerColor ATI Radeon X800 GTO16 256MB GDDR3 TV-Out/DVI (PCI-Express) - Retail (GX-055-PC)
£123.32
Total £489.57 including VAT.
Fast 3500+ CPU.
1 gig ram should be plenty, with 2 spare slots.
Good case with ATX 2.0 PSU
Very quiet DVD burner, i have one.
Good graphics for the price (just a bit slower than the X850XT, which you could add & only go slightly over budget).