I don't know anything about MSN, except that it was created by the dark forces. But in general, each user's environment is separate from each other. Generally, applications are universally available, but preferences are unique to that individual. There are tricks, however, that you can use if you want to share preferences (e.g. creating a link in the Terminal: man ln for more info; or perhaps even a MacOS alias will do the trick). You may have to tinker a bit with permissions to get it to work. I've used this technique to share a common set of iCab bookmarks amongst MacOS X users, and even with the MacOS 9 environment (which is on a totally different volume).