I could be wrong about this, but have you tried logging into the computer as admin and reinstalling internet explorer? Make sure you remember to enable access to other users as you see fit. I had a similar problem on my 32bit vista system with my internet explorer and also my world of warcraft. this actually solved the problem with my internet explorer.
Something else to keep in mind; vista uses virtual storage for settings for each profile on the computer. I found that i could use totally different mods for my different programs based on the login to the computer. Just remember there is a difference between altering these settings in admin mode and editing them in another profile that is LIKE an admin. I hope your issue works out and i hope maybe something i have said might be useful and accurate
good luck