I always install the latest version, which is 4.0.3 for 68k Macs and 6.0.3 for PowerPCs (OS 9) - is there any reason why you would use a version lower than the maximum for your Mac? I always assumed it was best to use the newest one as QT seems to be more of a core OS component on the Mac, not just a media player, and it tends to be best to update the OS core as much as possible. I always remove the FireWire extensions and things like that which come with the later versions and aren't needed on older Macs.