I downloaded the HL2 demo from Steam, both for OS X and Vista Bootcamp. Performance wise, there's no noticeable difference. However, there's a strange phenomenon in OS X. In the beginning of the game, you arrive at the train station where you can hear a voice welcoming you. There are also big displays on the walls that show the person speaking. In Vista, no problems, in OS X, those displays are just plain white, no animation. Could this be a problem with the demo or does the full game suffer from this too ? I have a 24" iMac with a 2.8Ghz Core2Duo, 4Gb of RAM, and a ATI Radeon HD 2600 Pro/256Mb card, running OS X.5.8.