MSN keeps signing out.


Hi all,
I'm a newbie in Mac, and would like to ask u guys to help me out on this case. I've installed MSN 5.0 from Msft site, after installing, i just sign in as usual, it can sign in, show me my buddy list, but after a moment (few seconds), it auto sign out with a message of "Unavailable service". Anyone knows the reasons (firewall, setting, proxy - i'm using proxy in my school, ...) plz enlighten me. Thanks for that.
And one more pro with me, i use PSI and setting iChat (in Tiger OS) to chat with YM, MSN by following exactly what i read from this website. I created succesfully acc from PSI, launched it, added successfully my YM and MSN acc (saw my buddy list in PSI). But when I open iChat, configured it, and launched it, it can connect; however my buddy list is totally blank !
Plz help me on those question, thanks all for that ! :)