Graphics card questions.

[υℓqυισяяα]

I just bought COD4, 5, 6 and Assassins creed and Far Cry 2
4 Didn't work [Pirated ]

And I just installed 5, but it says my gfx card/driver doesn't support Vertex data or something.

I will first try to update my gfx drivers, but if that doesn't work, I'll have to buy a gfx card, which brings me to this:

Can I install a brand new gfx card on my current motherboard? [Yes it has PCI Express slots]
What card would you recommend for playing the above games? Shouldn't be too expensive?

Thanks, arrgg, if only Santa would send me a gfx card for Christmas...