Thanks Ethel, I have just found a little program called aMsn which is just like Msn but with cam functions, still setting it up so don't knoe if it will work yet.
If you want webcam over msn, then amsn is about the only way to go on the mac right now I'm afraid. iChat is far better but doesn't support it totally (though I believe you could use jabber with iChat and pipe through to msn, but i've never tried it).
As ethel says, skype is another option, but that requires your friend to have skype too.