My Classic Support was broken on Panther. I re-installed it after doing an Archive and Install to Tiger. I'm not quite sure, but I think that if you Upgrade or Archive and Install from Panther (with Classic Support installed) to Tiger, then Classic will still be working (but the Classic System Preference might be hidden until you've run a Classic app for the first time). If you do a Tiger Clean Install you have to reinstall Classic Support, for sure.