IMac mic doesn't work in Windows?

My girlfriend has an iMac 8.1. In order to make it less useless, she installed Windows Vista Ultimate. Unfortunately when we use Skype or any program that uses the built in camera and mic, the mic volume is extremely low. I think it may be a driver problem, but I can't get into her girls-only dorm to check it out. She is decently computer literate, but simple answers are appreciated! What could be wrong?