Does your camera actually work? Try iChat to check that.
In Microsoft Messenger, does the camera not come on (the green light next to the lens will come on) when you click the Video Call button on the Contact List?
What version of Messenger are you trying to use?
I think Messenger does not support video calls at all until version 7 or newer.
Is your friend on a Mac, or on a Windows PC?
Try moving on to software that is more reliable, such as Skype.