If you installed all the drivers for Boot Camp, then go to My Computer > Apple iSight. If you can see a picture when you double click on that peripheral, then I think MSN doesn't have support for it. Otherwise, Skype and AIm both work for me.
Are u using this with boot camp or Parallels or VMware fusion?
Boot camp will give you the drivers, if you using VMware or parallels you can download the isight driver on the internet - I had to do this with my Macbook when i started using vmware