There are some web-based alternatives that don't require the installation of an MSN Messenger client. So as long as network administrators don't block these particular sites, you will be able to chat to your MSN contacts (although not with all the bells and whistles of the normal MSN Messenger):

NOTE IN ADVANCE: The sites below are all maintained by third party developers. Although most of them have been tested and have a decent reputation, it's up to you if you trust them with your e-mail and password. If you decide not to, then I suggest you use the official MSN Web Messenger.

Meebo
This web-based IM client allows you to sign into AIM, ICQ, Jabber, Yahoo! Messenger and of course, MSN Messenger/Windows Live Messenger. My personal favorite.

>> Go to Meebo.

eBuddy
eBuddy (previously Everywhere MSN or e-Messenger) is a webbased application created by Paulo Taylor and enables users to connect to MSN through a desktop browser or a mobile phone (or Palmtop) using cHTML/xHTML or WAP 2.0. The new version allows Display Pictures and has a layout very similar to MSN Messenger 7

>> Go to eBuddy

MessengerFX
Probably the youngest player in the game, but it works fine and surfs the AJAX wave.

>> Go to MessengerFX

MSN2Go
MSN2Go is the world's first free web-based MSN Messenger client to be created in the form of a Java applet. It's not another HTML/JavaScript hybrid, but a true Java applet that works equally on any Java-enabled browser. That means no page-refreshing whenever a user changes status, no JavaScript kludges, and no DHTML glitches and artifacts.

>> Go 2 MSN2Go [Reported by: DJ Bri T]

ILoveIM
MSNGER is the fifth web-based MSN Messenger compatible client we found out about.

>> Go to ILoveIM.com [Reported by: Doobies]

Removed from this page: WBMSN ("Clientless Conversations") by Jared  and Piglet IM by Jeroen Geerdink.

Opperator <opperator812@hotmail.com>
November 28, 2003 at 1:00am

Op school of op het werk, kan ik niet MSN Messenger installeren omdat het is geblokkeert. Wat kan ik doen?

Er zijn een paar website-gebaseerde alternatives die geen installatie nodig hebben om een MSN client te gebruiken. Zolang de Netwerk-Administrators deze sites niet blokkeren, kan je chatten met je MSN contactpersonen (maar dan zonder alle toeters en bellen van de echte MSN) :

#1. WBMSN
WBMSN ("Clientloze gesprekken") is een goede en popelair online MSN Messenger script bij Jared en is aanbevolen.

>> WBMSN [www.wbmsn.net]

#2. Everywhere MSN
Everywhere MSN or eMSN is een website-gebaseerde applicatie gemaakt door Paulo Taylor enmaakt het mogelijk om gebruikers verbinding te laten maken via een desktop browser of een GSM (Palm Top) door middel van cHTML/xHTML of WAP 2.0.

>> Everywhere MSN [www.everywheremsn.com]

#3. Piglet IM
Piglet IM is een 100% website-gebaseerde MSN Client gemaakt door Jeroen Geerdink en getipt bij mij door Brian Turchyn. Hij zoekt nog steeds zijn weg op de nieuwe server, maar het is het cker waard om te kijken.

>>> Piglet IM [http://piglet.0900provider.nl/]

Sagar <sagarkk@msn.com>
January 10, 2004 at 1:00am

Thanks

I'd like to thank whoever put this up on the site coz its been reaaalllly helpful since I cant install MSN Messenger from school.

Cheers to you :)

Toni
February 17, 2004 at 1:00am

You can try www.warpmessenger.com in french if you prefer. Bye

Braindamage
February 19, 2004 at 1:00am

Use an old MSN version

I found an answer to this problem when I was at school.

If you can't install the new MSN versions, then install an old version (found on this site), and by old I mean something like 3.5.

When the ports are closed, it's offcourse an other problem

Greetz

Avan
April 1, 2004 at 1:00am

Me either

I can't use MSN at school no matter I tried that three of the web sites which mess.be provided...can't go through those though>.

Rodrigo
June 13, 2004 at 1:00am

Maybe too suspicious

This informaton is great and I did checked WBMSN. Still, I'm a bit concerned about my password. After all, what prevents them from logging my username and password ?
Also, there is no sign of any security measures. Even if they're trustworthy, what about people hacking them to get usernames and passwords ?

Shadow_Master <optional>
July 8, 2004 at 1:00am

MASTER

please can someone make a online msn messenger service that changes url weekly or so to prevent the ability for it to be blocked by administraters e.t.c. as easily.
then post each url on a specified forum or something
thanks

Me <me>
July 30, 2004 at 1:00am

Me

Hey, this is a very helpful page, with useful links, and i ask that it is placed pernamnetly in the Information and Knowledge section of the site.

rodrigo. yea, its a matter of trust. do u trust ppl? if so, do this. if not dont do this!

although, i guess there is another option...

make another account, then just use that for web based MSN...and ur other account for home MSN. easy enough 2 do...

Rice

::deePsPace::
August 9, 2004 at 1:00am

M$ version of WebBased Messenger

Microsoft's own version is online (Beta) at
http://webmessenger.msn.com/