Dell dimension 4600 Graphics Card

I finally completed my mother board replacements ram upgrades and windows XP os reinstall's on me dell dimension 2400 and 4600 . bothe of these computers are running very fast for what they are.  the 4600 has a 2.66 in it and the 2400 has a 2.53  i am going to upgrade both of the CPU's for next to nothing from ebay. i play all of my old roms on these computers.  they just dont seem to like to run the PJ 64 rom and the super nintendo rom.  im suspecting this has to do with the onboard graphics card on both of these computers.  part of the reasons i brought these computers back to life was so i didnt have to go cartidge style.  any suggestions.  I know people have bumped these computers up quite a bit. but i think a graphics card and a CPU upgrade will really help me out now i need your help !!! i also have no clue how to burn an AVI  file to a DVD im a total noon about alot