Cannot install 64-bit iTunes (v10.5) on Vista
Did some digging because I knew I have seen this error before. It looks like it is not a direct issue with iTunes but with your Microsoft Virtual C++ redistributable. I resolved it by following the steps in http://answers.microsoft.com/en-us/windows/forum/windows_vista-windows_programs/microsoftvc80crtversion80507274053typewin32publick/c1359ee5-e18d-4512-8bff-890936db2810 

You are clearly not the only one having this issue, and the steps can be generalized to:


Run windows update
Download and update your Microsoft C++ redistributable http://www.microsoft.com/downloads/details.aspx?familyid=766a6af7-ec73-40ff-b072-9112bab119c2&amp;displaylang=en#filelist


That has worked for me for a couple of different people's problems, and I hope it fixes yours. 

There are additional steps in the thread such as some registry fixes for the windows installer service, however I would give these steps a try first, especially since they cant really cause any harm.