I've downloaded Windows 7, and i want to install it on my Microsoft Virtual PC 2007. But when I press Install Now, it asks me if I want to Upgrade or Custom. When I select Upgrade, it says, "To start the uprgrade, an existing version of Windows needs to be running. Restart your computer so that Windows starts normally and then restart the upgrade." And only thing I can do, is to click Close. When I select Custom, it can't find any drivers. I don't really know what to do, so please help me out. I really want to try Windows 7.