OK this post is going to fall into the ‘what the’ category. I just reinstalled Windows 7 Enterprise 64-bit on my MBPU and the iSight webcam is working inside Messenger! This is strange since last time the webcam worked in Windows but not inside Messenger. The only difference is that i installed Enterprise this time instead of RC but i cant see why that would make a huge difference as it is the same version of Messenger, which seems to be where the issue lies.
I will investigate further and keep you posted but the main reason i wrote this post is to point out an excellent utility i found for testing your webcam. Its very small and simple but provides a large range of useful information. The utility is called Webcam Diagnostic Assistant and it helped me to work out when i was using RC that the webcam was indeed working under Windows, but not inside Messenger.