I had a problem with iTunes 7.5 a few days ago, after updating it to the current version it would not start. Even after I try to install and uninstall it over and over again. This is how I got it to work just in case any one else is having the same problem.

1 Uninstall iTunes and Quick time.
2 Download and install iTunes 7.5
3 Uninstall Quick time {again}
4 download Quick time application and reinstall it

It seems to be a problem with Quick time within iTunes install package. After I did this it worked just fine

iTune 7.5 http://www.apple.com/itunes/download/

Quick time http://www.apple.com/quicktime/download/