Last night I  was able to view my media from my Vista machine to my Original Xbox. 

 Things needed:

1. XP Media Center 05 CD

2. Install http://www.microsoft.com/windows/products/winfamily/virtualpc/default.mspx

3. Microsoft Media Center Extender for Xbox

Download the Virtual PC software,  then create an XP MediaCenter image.  Install the XP Media Center 05 on that Virtual image (Make sure you install the XP Media Roll up update after the install). 

After you create the XP Media Center image, make sure you can see the Vista machine on the Virtual XP Media Center machine so you can grab those files later.  When  finished, install the Xbox Media Center software. 

Once thats all install and you can see the media on Vista throgh network settings.  Insert the Xbox Extender CD in your Xbox.

Should be in business then