Hi, well for a start, I don't think your processor needs upgrading, 2.8Ghz is pretty good. I do loads with my pc and I only have a 1.8Ghz processor.
If you have been happy with your graphics card up till now, and you don't have any problems, why change. If you have less than 2Gb of RAM, then that is what I would advise you to spend your money on - more RAM. If it aint broke, don't fix it.