Windows Media Center Edition (MCE) was launched in late 2002 as Microsoft's answer to seamless integration of your PC and your Home Entertainment System.  MCE has built in support to turn your PC into the connection point for your digital images, recordings, TV and music. The Media Center Edition is built upon the Windows XP Professional operating system and is currently in its' 2005 release. One problem that has been noted is the inability to use MCE 2005 in a networked environment with a domain controller. While most homes consist of a peer to peer type network with no domain controller, more and more homes with home offices are becoming wired and connecting all the computers to a home, domain based network. Here is information from an article from Raphael Rivera's blog site that gives instructions on how to hack MCE 2005 to allow it to join a domain. As always, remember to make a back-up of your current configuration and note that making any changes to your registry can render your computer inoperable.

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IMPORTANT NOTE: Tekmaven brings up a valid point -- Those that join a domain with Media Center 2005 will *not* be able to use extender devices due to the Fast User Switching dependency (who uses extenders anyway?)

UPDATE (January 8th): I have received news the Linksys MCE Extender device works fine when joined in a domain.

1. Insert Windows XP CD.
2. Start > Run > X:\i386\winnt32.exe /cmdcons
   (replace X: with the appropriate drive letter)
3. Acknowledge prompt by clicking 'Yes'.
4. Skip updating process by clicking 'Cancel' or by pressing 'Esc'
5. After installation, acknowledge success msg. by clicking 'Ok'
6. Start > Shutdown > Restart
7. At boot menu, select 'Microsoft Windows Recovery Console'
8. Select proper installation to log onto (default: 1) and press 'Enter'
   (If prompted, enter Administrator password and press 'Enter')
9. Type (without quotes) and press enter: 'cd system32\config'
10. Type (without quotes) and press enter: 'copy SYSTEM C:\'
11. Type (without quotes) and press enter: exit
12. At boot menu, select 'Windows XP Media Center Edition'
13. Log into Windows and play a game of minesweeper (very important)
14. Start > Run > Type: 'regedit' and press enter
15. Click on 'HKEY_LOCAL_MACHINE'.
16. File > Load Hive...
17. Browse and select C:\SYSTEM
18. Specify key name 'BANANA' and click OK
19. Expand: HKEY_LOCAL_MACHINE > BANANA > WPA > MedCtrUpg
20. On the right-hand side, double-click IsLegacyMCE value
21. Change selected value to 1 and click Ok. (THAT IS NOT AN L!)
22. Click on BANANA subkey (under HKEY_LOCAL_MACHINE).
23. File > Unload Hive. Confirm.
24. Start > Shutdown > Restart
25. At boot menu, select 'Microsoft Windows Recovery Console'
26. Take sip of Dr. Pepper (very important)
27. Select proper installation to log onto (default: 1) and press 'Enter'
    (If prompted, enter Administrator password and press 'Enter')
28. Type (without quotes) and press enter: 'cd \'
29. Type (without quotes) and press enter: 'copy SYSTEM C:\WINDOWS\SYSTEM32\CONFIG\SYSTEM'
    (Yes, you want to overwrite - Go ahead and do it)
30. Type (without quotes) and press enter: 'del SYSTEM'
31. Type (without quotes) and press enter: 'exit'
32. At boot menu, select 'Windows XP Media Center Edition'
33. Take a break while you wait.
34. Join domain. What, you were expecting instructions on this too?

Thanks goes to Chris123NT, Dyne, Creamhackered and LispyGlitter2

http://www.extended64.com/blogs/rafael/articles/404.aspx