Hmm... There's only once place where it could throw that error, and it's rather unlikely that anything would go wrong in that particular section. Let's see if we can find the problem. First, some more information please:
- What is your exact Windows version?
- What userlevel are you? (Administrator user, normal user, with or without UAC?)
- Please paste the contents of intall.log (should be in the same dir as the installer, when installation fails)
Unless the last entry in that file is "Extract ..a", I can't think of anything specific that might cause this problem, to be honest. Here's a random idea: Try installing with your virusscanner disabled, see if that changes anything.