I need a new gaming pc within the budget.
Some parts I already own and can use in the new build:
Geforce 8800 gts *(unless I can get a better card with a huge improvement within the $600 budget)
dvd/dvd+rw drive
450w power supply
Microsoft Windows 7 pro 64 bit OS
Monitor
Mouse/Keyboard
Speakers
I like to use www.newegg.com for ease. I do not need it to look fancy or quiet, just the best gaming performance for the money.



cpu: Phenom II X4 965 http://www.newegg.com/Product/Product.as…
mobo: MSI 880GM-E43 AM3 http://www.newegg.com/Product/Product.as…
ram: 2x2GB DDR3 1600 CL7 http://www.newegg.com/Product/Product.as…
gpu: Asus GTS450 925Mhz http://www.newegg.com/Product/Product.as…
hdd: Samsung 1TB 7200 http://www.newegg.com/Product/Product.as…
case: Cooler Master CM690 II http://www.newegg.com/Product/Product.as…
total: precisely $600 (without shipping)
psu & dvd drive can be used
i5 750
Cheap H55 1156 motherboard (£50-£70)
cheap RAM is fine
you should get a better than 450W psu… £30 a decent 600W you could get