Regarding Firewall proxy and MSN messeng

Can someone tell me how to get going with MSN when you are behind a corporate fire wall…?
well I succeded in doing it with Yahoo messenger, but still unable to find a way for MSN. For my yahoo messenger i am always using http server 10.10.60.9 port 4480 . But it’s not work in MSN Messenger i have tryied all the way i need solution for this. i am really very thankfull to you if i can get solution as early as possible.