I need to use the same Parallels virtual machine (with Windows 7 Professional 64-bit) on a MacBook Pro with two disk partitions that can be booted into Mac OS X 10.6.8 Snow Leopard or Mac OS X 10.7.2 Lion. I have installed the Parallels software under both partitions (Snow Leopard and Lion). But when I launch the virtual machine under Snow Leopard, it immediately starts installing the Parallels Tools (telling me it's not installed correctly) and demands a restart. The next day I'll be starting the virtual machine from under Lion, and it will automatically start installing Parallels Tools all over again and demanding a restart. The next day I'll be starting it from under Snow Leopard and it will automatically start installing Parallels Tools again on top of the Parallels Tools already installed there. I'm losing a lot of time and experiencing a lot of frustration. What's the best way to deal with this situation? How can I prevent Parallels from automatically installing a new version of Parallels Tools each time I boot up the virtual machine from a different version of Mac OS X?