Right,
Got one for you, very similar to the Gaming (alright, Sims 2) rig I built my mother in law a couple months back. That came in under budget, but I didn't need a Case, DVD Writer or Hard Drive.
Prices are a little better now, so my suggested build is thus:
All from Ebuyer UK (
http://www.ebuyer.co.uk)
1 x AMD Athlon 64 X2 4200+ Socket AM2 (2.2GHz) L2 1MB (2x512KB) Retail Boxed Processor 118226 £46.73
1 x Asustek M2V AM2 VIAK8T890 Sound, Gigalan And USB 2.0 2000MHz FSB SATA ATX 112169 £39.33
1 x ASUS X1950 Pro 256MB GDDR3 DVI HDCP HDTV out PCI-E Graphics Card 131876 £81.95
1 x Arctic Power 500W PSU With PCI E, SATA, 20+4, ATX12V, 8pin +12V Connectors Retail Boxed 124922 £24.99
1 x OCZ 2GB Kit (2x1GB) DDR2 800MHz/PC2-6400 CL 4-4-4-15 PLATINUM XTC with LIFETIME WARRANTY 116755 £59.99
1 x Western Digital WD1600JS Caviar SE 160GB 7200RPM SATAII/300 8MB Cache - OEM 94406 £31.54
1 x Samsung SH-S183 SATA 18x DVD±RW/RAM Black - Bare Drive OEM 127260 £17.62
1 x Casecom 6630 Black Midi Tower Case With Front Panel USB2.0 Audio No PSU 119589 £11.99
Total Price: £302.15 (Plus Delivery)
The 5 or 6 digit numbers are the "Quickfind" Numbers for those parts, pop them into the search box on ebuyer and the part will come up.
I included 2Gb of OCZ 800MHz RAM, as it's a little more future proof than the Corsair 2Gb 667MHz Kit I looked at (Quickfind 98708: £49.99)
The Power supply could be better, but it's double the price I paid for my mother in law's (Quickfind 126928: £15.31) and that runs this system fine.
The Motherboard is a nice AM2 Part. Nice and stable, runs the 4200+ Like a dream.
My Mother in Law's system has a 7600GT, but for an Extra Tenner, you can have a nice X1950Pro 256Mb. This will handle most games at 1280x1024 with fair to high settings.
BioShock (for instance) runs really nice on my mother in law's system at max settings, so should run fine on this.
Hope you like.