Another thing I can't stress enough ~(I've made this mistake TWICE).
Be careful of the type of card you get in relation to your computers power limits.
On two occassions I've gone out and bought myself a spanking new graphics card, only to come home plug it in and the computer shut down soon as it has to do any work.
Leaving me with the option of returning the card (pfft.. I don't think so
) or upgrading.
If your system can take PCI-E, I "STRONGLY" recommend you go there.
Visit some review sites that test cards and have a read, like here.
But remember your graphics card will only work at full potential/or at all, if your computer can handle it.
So find out what your power supply is, if your mother board supports AGP or PCI-E and the size/age of your monitor (for resolution).