Microsoft has released the February 2008 Cumulative Update for Media Center for Windows Vista. I would expect the update is included in Service Pack 1 for Vista as well as being on Windows Update

Fixes include:
Addresses an issue that is introduced in KB941229 in which the UI freezes and becomes unresponsive. This issue occurs when you try to change the channels while you are watching live digital TV on Xbox 360.

This update replaces the 941229 (http://support.microsoft.com/kb/941229/) October 2007 Cumulative Update for Media Center for Windows Vista

It will be on Windows Update

Download the 32bit version
Download the 64bit version

More details from Microsoft: February 2008 Cumulative Update for Media Center for Windows Vista