I just got the Update rollup 2 for Windows Media Center Edition 2005, it's available at the Microsoft OEM syste builder site, at the end of month it will be released to the regular Windows Updates. The following components need to be preinstalled:

1. Windows XP Media Center Editon 2005
2. .Net Framework 1.1 Update
3. .Net Framework 1.1 Service Pack 1 Update
4. MCE 2005 rollup 2 Executable

Thanks to Oriveradel