On his blog Matt Goyer notes:
You don’t have to wait for Vista for some bugs to be fixed. Get the July rollup for fixes to Media Center 2005. What does this fix?
Horizontal white lines appear when playing a DVD
Media Center may crash when using the ListMaker SDK sample application
Media Center may crash when you open a menu page
A black screen appears when trying to play a DVD
There more details in the kb article
I've seen the white lines problem on a colleagues PC so I'll be able to check that fix out later today.
Good to see that in all the rush to the Vista version 2005 users haven't been forgotten.