I knew I should have listened to them. I went ahead and tried to install iTunes 5 + Quicktime on my office computer and, sure enough, I had the problem where the installer hung up with an error 1628. I deleted everything from the ~User\Local Settings\Temp folder, restarted and tried reinstalling. It seemed to go swell. It was a bit scary at first, but everything seems fine. If you have the same problem, try my fix.