Your approach is flawed. Copy the things that you need to backup and do a clean install. Vista has a bloated registry out of the box, let alone how bad it must be after years of use. I get that you don't want to spend the time re-installing your needed software, but ultimately I think you'll spend more time trying to do an upgrade, which may well result in a corrupted OS that needs to be re-imaged anyway.
"There are three kinds of lies: lies, damned lies and statistics." - Benjamin Disraeli