Well.. and more exactly where you live. But you can order the parts from internet.
My opinion if youwant for games you can use :
~AMD CPU Phenom II 965 Black Quad Core Processor Black Edition, SOCKET AM3- it is around £106.42.
~AsRock N68C-S UCC GF7025 DDR2x2/DDR3x2 AM2+ M-ATX Motherboar - N68C-S UCC -cost around £35.47.
~Corsair 8GB (2x4GB) DDR3 1333MHz XMS3 Memory Kit CL9 1.6V - cost around £67.95 Ex VAT.
~ ATI FirePro V4800 Graphics Card - 100-505606 - cost around £117.12.
...and there you have a desktop computer.:)
And with this you can play games for at least 4 years from now on... I mean good games with high requestments. And you can use it for multimedia too.. for example you can use all Adobes software's , Pinnacle Studio, Magic Studio , and many others. and it will be pretty fast when you running lot's of programs. :) all that left to have it will be a big HDD.