When it pops up the install dialog and suggests a folder/directory for the install, what directory does it suggest?
I'd be interested to see the full path that it suggests. If you can reproduce up to that point in the process, please post what it says. It might give a clue and get us farther along in the troubleshooting Leesifer, ceptimus and Sauron have suggested.
Why isn't this thread in Computers & Technology forum? It might be worth a move -- maybe there'd be more techy help if it were there?