Microsoft's press release about Media Center on the XBox clearly states that an Exctnder should be able to play copy-once and Live TV content from my Windows 7 PC. If this is correct, then there is a definite problem here. If I start watching live TV and navigate to CBS HD, I get the dreaded "copying prohibited" message on my XBox. This content plays fine on my Windows 7 Ultimate PC. Also, once I've navigated to a copy-once channel, all subsequent channels give me the same message until I turn off and turm back on the Xbox. After that I can watch TV on the Xbox until I navigate to a channel that is copy-once.
I'm running everything on a local network and I'm using the HDHomerun Prime with a CableCard to tune in TV.
I can't find anything about updates to Win 7, the HDHomerun or Windows Media Center that might solve this problem.