How do I use windows live messenger or msn or windows messenger without downloading it?

use webmessenger

http://webmessenger.msn.com/

How do I use windows live messenger or msn or windows messenger without downloading it?windows firewall

Well if you haven't got the program itself then you cannot use it but you can download it very easily by going to this site http://get.live.com/messenger/overview

How do I use windows live messenger or msn or windows messenger without downloading it?microsoft frontpage internet explorer

go to

http://www.ebuddy.com/index.php

Its an internet browser version of messenger.
you have to download the source and install the program on your computer, besides windows messenger is installed with your windows version