Vista - US English XBOX 360 + US English Vista Beta 2 = Broken Media Cente

I have a US NTSC Xbox 360 and a US English copy of Vista Beta 2. When I try
to use my 360 as a media center extender, Vista will error out after it tries
to connect to my 360. My 360 stays on the black screen where it keeps trying
to connect to the Media Center.

All this happens after I enter the 8-digit code on the PC, during the
"configuration" phase of Media Center where it tries to upload the user
settings to the extender. I've tried it with and without uploading the user
settings and it does the same thing every time.