I never even bothered to upgrade a windows install, i always just formatted and did a clean install. I didn't trust windows to upgrade a installed OS at all. I have a new mac pro on it's way, and it will arrive with Tiger. That being said, after a few months of getting all my files and everything sorted out after the switch, will I be able to install Leopard without many adverse effects? Or will it be necessary to wipe the hard drive and reinstall eveything? I have no experience at all with installing an OS on a mac, so I'm a little nervous, since I'm moving all of my work/business over from XP to OSX, I want to be able to move to Leopard as easily as possible, but also maintain my systems stability. I know I *can* do an upgrade from 10.4 to 10.5, but will it be as reliable as a clean install of 10.5? I know with windows, I wouldn't even bother attempting it.