Unless windows 7's installer is a piece of shit, which is possible, it should give you partitioning options, as well as what partition you want to install the OS in, which would be the C partition. Again, if the installer doesn't blow, you should be able to install Windows 7 without touching the D partition, unless it tries to make its own, which is possible. Regardless it is somewhat moot since that back up partition is for your Vista backup. If you have an external HD, it's best to back up your personal files on that. Then reformat the whole HD, and let the installer do what it does. I'm pretty sure it will give you an option to partition your HD again, so you can have a backup partition. In my experience, a lot of backup drives don't hold a lot of your personal data because of size restrictions. It's basically an emergency recover that saves all the essential files to run the OS correctly. If it were to have all of your personal files, it would have to be the same size of your C partition. I have never personally used a backup drive either. I'm much more comfortable just doing a fresh install after backing up anything I want, but that is me.