According to Microsoft the KB977863 deals with the following:
Issues that this cumulative update package fixes
The February 2010 Cumulative Update for Windows Media Center for Windows 7 resolves the following issues:
Improves the overall experience for systems that are configured by using digital cable card tuners.
Resolves backward compatibility issues for some legacy Windows Media Center extensibility applications.
Resolves an issue with how recorded TV shows are managed when switching to a user locale that is based on the Hijri calendar.
Improves the overall experience when you use Integrated Services Digital Broadcasting (ISDB) tuners. ISDB is a Japanese standard for digital television and digital radio.
However if you a domain user, domain consist of ISA, this update can screwup your happiness for a long while! Uninstall it, you don’t need it. Uninstall and try to install it once again, Microsoft will state you don’t require this update any further and you will not be annoyed by seeing the yellow triangle overlayed over the network connection stating “no internect access”
Applies to Windows domains with ISA proxy server.