I would say that most PCs these days are able to take an upgraded graphics card, I think it highly unlikely that it would not. If you know what you are looking for you could open the case and look for an AGP slot on the motherboard, or you could download a computer audit program to see what hardware resources are free. Whatever the case, if you install another graphics card you will have to go into the BIOS to disable the onboard graphics.
Thanks for all help guys. Just i have an old computer which has a 64mb Nvidia graphics card and im looking to buy a new computer and want to get a decent deal and i thought well if it comes with on board graphics but a decent deal then i would just upgrade and put my own graphics card in (obviously beter than i already have) thanks again guys!