It's easier to not deal with wine etc. It works fine for me with native Linux firefox, and mplayerplug. The trick is to login to mlb.com first, then go to the multimedia list to select your game from their. If you try to launch the flash first it won't work. The mplayerplugin will launch in a new small window so you can even full screen it if you'd like.
1. Add noembed=1 to $HOME/.mplayer/mplayerplug-in.conf
2. Using native firefox (linux version), go to mlb.com and at the top of the page log in. The key is to log in first.
3. Then select a game and mplayer will launch a window.
This must be the secret, i dont have a password for the site but it makes sense.
Tried to tell him that, but he was too dense to comprehend.