We've found that iTunes 8 is crashing Vista, or iTunes won't install at all. The main error states: "Itunes installer completed - The installer encountered errors before iTunes could be configured..."
We've found a solution, but this may not work for everybody. Here's a really good link to help you through the steps - http://support.apple.com/kb/HT1926?viewlocale=en_US
Make sure you use the recommended tool to remove any traces of iTunes on your system before taking the next step which is...simply...
...don't install iTunes 8 - use version 7.5 instead, downloadable from www.filehippo.com - of course, search for iTunes 7.5.
If anyone else has any recommendations, please feel free to post here.
The Geeks Admin