I have now changed the email address associated with my MSN account. It is now the same email address as I use for Jabber messaging: geir-tore at jabber dot no.
So now I can be contacted with the same address on email, Jabber (incl. Google Talk) and MSN.
_Update:_
It seems to be some trouble with changing the email address associated with the MSN account. I can log on to MSN with Messenger and my entire contact list is in place, but the online/offline status doesn’t seem to be updating. I have sent an email to MSN Support about the issue, but I honestly doesn’t expect a reply anytime soon 
Let’s hope that it resolves itself soon.
_Update #2:_
It looks like the online/offline status are propagating correctly now. It started to look right yesterday, after I sent out an email to all the persons on my contact list about the change, but I have confirmed that at least one of them didn’t update anything manually so there is somehow an automatic update process here.
[tags]msn, email, jabber[/tags]