If you have Alcohol 120%, Deamon Tools, or any other virtual drive software installed, try uninstalling them before trying to install 7. I had a problem with an IDE Controller driver that was caused by Alcohol 120%.
I was in the middle of upgrading Vista Home Premium 32bit to Windows 7 when the installer told me I needed to update the drivers for my IDE drive. Well, I don't have any IDE drives, and my IDE controller is disabled in bios, so I found that strange. Looking in device manager, under Storage...