Graphics

I'm in the market for a new graphics card, i now which one i want

http://www.amazon.co.uk/XFX-8800-500...7845019&sr=1-7

but does the power supply affect it at all? ive heard it can if you have a SLi but i dont now if thats true.

The power supply will *not* affect the output of the graphics card itself, not counting minor noise - although I don't think that'd be noticeable. That's only really relevant with sound cards.
The power supply will, however, affect whether it works, particularly in SLI/Crossfire setups, which are power hungry at the best of times. If you're just putting a single card in, though, you should be fine, as long as said power supply has a PCIe power output. Which it should.
That said, I would go for two SLId 8800GT cards for a little more than one of them unless there is a function of the GTS which isn't available on the GT.. Which I don't think there is. I may be wrong there, though.

so it really doesnt affect it unless i use a SLi setup?

As long as it has sufficient power to support the card(s) it wouldn't affect it even if you did have SLI.