You might have to go pre-built for the price and accept that games are a bit unrealistic at the moment.
For what it is worth this is about the best I can do for the budget, it offer a reasonable amount of overclocking potential considering the price.
Abit IP35-E (Socket 775) PCI-Express DDR2 Motherboard £54.99
(£64.61) £54.99
(£64.61)
GeIL 2GB (2x1GB) PC2-6400C4 800MHz Ultra Low Latency DDR2 Dual Channel Kit (GX22GB6400UDC) £34.99
(£41.11) £34.99
(£41.11)
Antec NSK 4480 Mini Tower Case - 380W Earth Watts PSU £45.99
(£54.04) £45.99
(£54.04)
Microsoft Black Value Pack 2.0 - OEM (S82-00029) £12.99
(£15.26) £12.99
(£15.26)
OcUK Value Hanns-G HW173A 17" Widescreen LCD Monitor - Silver/Black £89.99
(£105.74) £89.99
(£105.74)
OcUK ATI Radeon X1950 Pro 256MB GDDR3 HDTV/DVI (PCI-Express) - Retail £59.99
(£70.49) £59.99
(£70.49)
Hitachi Deskstar 7K160 160GB SATA-II 8MB Cache - OEM (0A32728) £25.99
(£30.54) £25.99
(£30.54)
Intel Core 2 Duo E2140 "LGA775 Conroe" 1.60GHz (800FSB) - Retail £36.99
(£43.46) £36.99
(£43.46)
NEC AD7170A 18x18 DVD±RW Dual Layer ReWriter (Black) - OEM £13.99
(£16.44) £13.99
(£16.44)
Sub Total : £375.91
Shipping cost assumes delivery to UK Mainland with:
City Link Parcel Next Day (Delivered Mon-Fri)
(This can be changed during checkout) Shipping : £12.95
VAT is being charged at 17.5% VAT : £68.05
Total : £456.91