Well, the reason that you can't see an IP over MSN is that, so long as you're just chatting with them, MSN routes that traffic through servers, you don't connect directly to the computer you're chatting with. Which means if you look for their IP, you're only going to get the server.

If you add voice or video to it, though, then it direct-connects, and you'd be able to see IPs. Then if you netstat you can find their real IP, if you can figure out which one it is.

I'm pretty sure this has been covered before, I remember reading it here somewhere long ago and far away.