I found a somewhat inconvenient workaround, but it appears to work.
Essentially I'm using Orb on a WinXP computer to relay the authorized URL for the stream to my PPC - not the stream itself. Here's a quick howto (sorry if it's very rough)
Prereqs: mlb.tv account, Orb (I use 2.0), Orb server and client set up to stream with windows media (asx).
Limitations: The authorization to start streaming times out quickly (just as on the desktop). You have to start streaming to the PPC ASAP (this was the bottleneck). Once you start the stream, don't stop it since orb is relaying the URL, not restreaming the stream.
1. Start Orb on PC and login. Make sure you tell orb to remember you, your password, and auto log you in.
2. go to mycast.orb.com on the PPC and login and tell it to save your password and autologin - I use PIE instead of Opera just because it's faster - and go to TV->favorites (I think)
3. Back on the PC, under TV->Internet TV add a new custom channel. Leave the URL blank, but do not close the add favorite dialog yet.
4. On the PC go to
www.mlb.com and select the game you wish to watch
5. If you haven't logged into mlb.com for a few minutes, it should ask you for your e-mail and passowrd.
6. IMMEDIATELY after you are authorized and the mlb media player turns black for buffering, right click on the video window and select properties.
7. IMMEDIATELY copy the URL (it should start with mms:// and your IP address should be near the very end) and paste it into the URL box in the add favorite dialog in Orb and hit OK.
8. IMMEDIATELY after orb is done checking the URL, on the PPC refresh the mycast page with the custom link (should be internet tv)
9. IMMEDIATELY tap on the link to the mlb stream
If you did everything fast enough, WMP should open up and the URL should change from "http://..." to something like "<date> : <away team> at <home team>" and then start streaming.
Note: If you've already set up an internet TV favorite, just edit the URL in orb instead of creating a new one, just remember you have to refresh the page on teh PPC to send you the correct URL.
From the number of "IMMEDIATELY"s above, you can see that it is important to do everything quickly. The clock starts ticking as soon as the URL for the stream is retrieved so have the Orb and the PPC ready to go - I even keep the mycast.orb.com page with the custom channel on it open and refresh selected from the menu.
I have not had luck e-mailing the stream's URL (which includes all the authentication) to myself and clicking on the link in my mail on the PPC. Nor have I had luck with editing a file on my PPC with the mms URL from the PC from which I log onto mlb.com. Maybe I was too slow, or maybe since orb checks the url, it keeps it alive longer. I stumbled on this trying to get orb to relay the stream itself from the PC to the PPC, but it appears, quite reasonably, that orb just relays the url instead of capturing and reencoding the stream.
Hopefully there's no real way for mlb.com to tell this is going on as they are planning on rolling out live video feeds, supposedly to WM5/WM6 devices in addition to the Java phones, this playoff season for an extra charge.
Anyways time to get back to watching the Indians and Twins!