Don't mean to necro this again, but it needs to be rectified.
"It's not going to happen. you can't install two O/Ss using the same directories. It might still be working, but it is screwed up. you can't install applications from one O/S and expect the other to still work right when they're both in the same directory. It just can't work. It might be working for you, but it's definitely not correct."
If you don't know what you are talking about it'd be better if you just stayed quiet, sorry to sound rude. You are correct, though, you can't install it into the same directory. However you CAN install it into a different one during the installation. I currently have Windows installed in c:\windows AND c:\windowsX.
You can install many copies on one HDD
Perhaps it's better not to assume? I'm still looking for a solution to uninstall my WindosX installation and user profiles, too. My next step will be to try deleting the WindowsX folder under a CMD prompt with System privledges. If all goes well I'll report back..