Don't go for socalled portamessengers, msnm messenger needs certain keys in the registry to work. These portamessengers will make these keys in the registry and are unable to remove them properly.
This has been discussed in previous threads:
Risico Messenger
[Updated] Messenger Live! Released [11 May 2005]
Portable Messenger
Also see "
Cookie's reply to Portable Plus"
If you can't use msnm on a comp go for webmessengers.