Intel Macs do not have drivers for the iSight camera. But as long as there's a Windows driver for the USB camera you choose, XP should be able to use it. MSN may have a limited list of supported cameras and/or formats, so check into that.
Note that "a BOOTCAMP/XP environment" is kind of a misnomer; all Boot Camp does is set up the computer for dual booting. If you're running XP through Boot Camp, you're running XP. Period.