Dude, your PC isnt that bad. 3.0GHz is cool, i would upgrade the RAM for sure.
If it was me, i would get a new motherboard to support Dual Core (i doubt yours does) get an AMD X2 CPU, cheaper than intel, and some 800mhz ram, corsair are the good. Also, if you want gaming then a new graphics card would be useful. This should easily be under £300 because you wont need a hard drive or other parts, you might look into a better PSU aswell, ask Cabe what he thinks on that.
Click here - to see my specs on the PC im getting. May be of some help.
Kev
