Ever since installing Divx 6 I have been dealing with having my MCE focus stolen (and the screen flickers that come with such) every time I even so much as go into a folder that has Divx-encoded files. I found that a little taskbar Divx icon came up that caused this so after a little research I found the following registry entry that prevents the icon.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\DivXNetworks\DivX\SMExclusions]
"Media Center"="ehShell.exe"
Add that registry key and don't worry about that stupid taskbar icon annoying you anymore!
*This registry entry worked for me but I can in no way guarantee that it will work for you so, if your Media Center blows up please don't blame me