My brother gave me his old Linksys Extender, but the installation CD wont run to the end.  TGB pointed me to download XboxMCEFULL-ENU.exe  and when I run that, I get this error:

Setup Error

There is a problem with the installation of Windows XP Media Center Edition 2005.  Uninstall the update to Media Center Edition 2005 and then re-install the update from the Windows Update website.  Then run Xbox 360 Setup again.

 

What should I do now?  How can I get this extender to work without the CD?

If you have the install CD key, then you can use this download. It's the entire CD of mine in .iso format.

I've ran across this same problem.

I think this is your issue. 

 

http://jtsang.blogspot.com/2008/05/windows-xp-sp3-vs-media-center-2005.html

Good catch!