Unfortunately, the Leopard upgrade doesn't transfer all the settings that Fusion requires, so Fusion has to be reinstalled after the upgrade.
So the best way is to upgrade to Leopard first, and then install Fusion 1.1 over 1.0.
You can also uninstall Fusion 1.0 before upgrading to ensure a clean 1.1 installation.
The uninstaller doesn't remove any of your virtual machines, just the application.
