Thanks!
The likeliest possibility I can think of based on your symptoms is damaged Apple Application Support program files. (Much like iTunes versions 9.0.x, iTunesHelper requires a properly functioning Apple Application Support in order to work correctly.)
*Assuming that you don't have a Safari for Windows version 4.0.5 installed on that system,* I'd try the following technique with a 32-bit Vista:
http://discussions.apple.com/thread.jspa?threadID=2256037
*If you have a Safari 4.0.5 installed on the system* we'll need to try something different. (We need to make sure that you have an Apple Application Support 1.2.0 on the PC in order for Safari 4.0.5 to work ... at the present point in time, the procedure I outline above will only put an Apple Application Support version 1.1.0 back on your PC.)