I played StarCraft, Rainbox Six: Rogue Spear, The Sims (hah!), all on my old iMac Sage 450MHz with 512 RAM, all perfectly well.
Right now I've got the TFT 700MHz with 786 RAM, I can run StrongHold wuite nicely (way better than my PC friends can, for the most part). This beast can do anything...