The first thing to try is a disk check as that kind of error suggests disk/file damaged.
But before that could you post the error message in full, exact text please. Sometimes a specific file is mentioned.
Running a disk check:
Although this is vista, window 7 is the same.
It takes quite along time to do a full check so best to do it when you don't want to use your PC.
Did the disk check find and fix any errors, if so try installing iTunes.
If you still have the problem we will need to dig deeper.