blah,don't listen to him,just get whatever type of graphics card you want,I got Ati because it just seemed easier to tell which graphics card where better than others. But go with whatever you want.
That is the absolute wrong thing to do.
BTW, you'd be better to get a video card moreso than a new processor.
First thing you are going to have to check is whether your motherboard has a PCI-E slot or AGP.
We can go from there. If you want, you can post your motherboard model here and I'll find out for you.
