I don't think Macbook video chat works with MSN nor Yahoo Messenger. I tried it but it didn't work. Skype video conferencing/chat works with MacBook. Go for Skype.
zarly, have a read of this. You will be able to use iChat to communicate to your MSN buddies via text + iSight if you have one. No audio, that's the catch.
http://www.mac-forums.com/forums/showthread.php?t=49157&highlight=isight+msn
http://www.mac-forums.com/forums/showthread.php?t=42004&highlight=isight+msn
http://www.mac-forums.com/forums/showthread.php?t=42449&highlight=isight+msn
http://www.mac-forums.com/forums/showthread.php?t=38624&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=34175&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=34621&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=33574&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=31537&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=26005&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=31441&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=30930&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=30825&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=28647&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=13418&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=15877&highlight=msn+isight
http://www.mac-forums.com/forums/showthread.php?t=27012&highlight=msn+isight
Oh, and before I forget:
http://www.mac-forums.com/forums/search.php
The above page is meant for being used.