iTunes 10.5.1.42 download corrupt

I'm trying to install iTunes 10.5.1.42 on a Windows XP machine running Service pack 2, and I get the error

"There is a problem with this Windows Installer package. A program run as part of the setup did not finish as expected. Contact your support personnel or package vendor."

I've tried to download and save the file, download and run and I get the same error. We need the new version installed so we can update our iPads to IOS 5.

Ideas?