buy a new video card or just a new pc???

[yeahme]

I have been struggling recently with my pc that I have had for about 5-6 months as when I bought it I was using it for work such as Microsoft word and excel but now as I have stopped working at home. I am now using it for games and the like but my vista performance rating is a mere 2.6 being dragged down by a miserable aero performance and my gaming graphics rating is only 3.1
The last three games I bought, (command and conquer 3 Tiberium wars the Kanes wrath expansion pack and supreme commander) and all of these have within minutes gone into a non responsive state. but to buy a new graphics card i'm looking at the vista rating of 4 just for the command and conquer games and that is looking at a price of around £170 to £200 and the reccommended vista ready card on the ATI site is "3650PE1GB Diamond Radeon HD 3650 GDDR2 1GB Dual Link DVI, Native HDMI, VGA
Bus Type: PCI Express x16" £179.99
money that I don't have lying around when to get the full advantage i will be needing a new processor and extra RAM and maybe a new motherboard to do all of this on

do any of you have any suggestions of what i should do and maybe somewhere that i can get this stuff from that is reliable and good value

confused outta my mind

cheers