I've read the posts concerning sound issues under Boot Camp. They all seem to point to a lack of volume. My situation is the reverse - the volume is much too loud on the Windows side. I'm forced to turn the system volume down to under 20 percent. Even then, application volume settings have to be set to near the minimum as well. This applies to iTunes, Windows Media Player, Flash videos and so forth.
21.5" iMac Boot Camp 3.2 Windows 7 (64-bit)
21.5" iMac, 20" iMac, iPad, Mac OS X (10.6.6), Daffy Duck mousepad