I successfully did an upgrade install (but not from Vista, although I have heard of many success stories upgrading to 7 from Vista). However, that said, a clean install is of course the best way to go, but 7 has improved the upgrade process considerably over the past versions of Windows, so if you have a lot of programs and settings, imo, it is worth giving an upgrade install a try. If it doesn't work out, no harm no foul, assuming one has made a good backup before starting on this. One can always do a clean install if the upgrade install doesn't work out satisfactorily.
Anyway, if you want to keep your programs and settings, you could give one more try at doing a "repair install
." And if that doesn't work, then go ahead with the clean install (and consider using the Windows Easy Transfer utility to help with migrating data and program settings). If you want to try the repair install, specific instructions can be found in the tutorial section of this forum: Repair Install
Also, you can find instructions on how to use Win Easy Transfer in the tutorials.