This is kinda just a bump b/c I'd like to know too.
But, I tried to navigate MSN & MLB's pages yesterday to find an answer w/ little luck. Interestingly, though, MLB.TV's site does include the following in their Subscription Acess FAQ:
12. MSN Premium or Dial-up Subscribers.
If you are having problems or issues accessing your new subscription, it may be a problem with your MSN account. Please visit MSN Member Services for assistance. (http://mlb.mlb.com/NASApp/mlb/mlb/help/ ... ns.jsp#q12
So, at least there appears to be some connection. If I could have found an email at MSN, I would have emailed them and asked. But alas, Geeky Billy Gates has hidden his employees behind the curtain. Can anyone else find out?