Install Script Engine is missing

I am on Windows XP Pro w/SP2 installed. I am trying to download the latest iTunes as I just received an iTunes Touch. I get the following: The Install Script Engine is missing from this machine. If available, please run ISScript.msi, or contact your support personnel for further assistance. I have gone to Common Files-InstallShield-Drivers and deleted 11 and re-downloaded and re-installed it as directed on the support page for re-installing ISScript engines,and I tried to re-install iTunes, and received the same message. What did I do wrong?