[Darvince]

Often what I do when I try to play games, as I have never had a very good computer, is to shut off all the other programs that are running before opening the game. For many, it enables me to play them at all. If SimCity 4 has good performance when you run it right after you restart the computer, I would first blame Firefox, especially if you have many tabs open. Many websites these days are very resource intensive only because they can be, running all sorts of unnecessary and poorly coded scripts constantly.