What kind of 2.4ghz machine? If it's an iMac
Warcraft runs good, Spore runs pretty good, World of Goo is great, Civ IV is good, Worms is good (nostalgic), Need for speed carbon runs good. <<These games are on the highest visual settings possible.
Command and Conquer runs pretty good, on medium to high settings.
And if you can find a torrent version of Kane's Wrath (they never released it for mac, so somebody cider'd a windows version) This game works perfect on all settings, he did a better job than EA did.