block MSN Messenger

["Bruyere, Michel" <mbruyere () ezemcanada com>]

Hi, 
        I would like to know the best way to block the MSN messenger
program. I used the policie that do not allow to run windows messenger
and it only works with the built in messenger. I would like to block ALL
versions. 

I actually have few ideas, like null routing the msn servers or things
like that but I would like to know how you guys did it. 

NB: if you have tips for others IM like yahoo or AIM, I'll take them too
;)

Thanks for your inputs