Which oracle should I download for windows 7 x64?
I'm re-reading your post, trying to determine if you're having problems installing 10g, 11g or both.  Whichever, I found an article on how to install Oracle 11g on Windows 7, describing the problem that you're having above.  Basically, the installer should present you with an option to override the prerequisite OS check.  Follow the link, go to step #3 and see if that helps you.