I recently reloaded Windows XP Media Center Edition 2005 to Windows XP SP2, so I could join it to a domain. This was before I realized that XP Media Center 2005 could be joined to a domain! Grr!! Much time wasted and a somewhat unhappy customer seeing as people don't like change... I wish I had run across this article sooner!

I give all credit to the author (whomever that may be...) but wanted to keep track of it for my own personal record keeping.

1. Insert any Windows XP CD.
2. Boot to the CD and choose Recovery Console
3. Select the installation to log onto (default: 1) and press
   Enter. (Most likely the administrator password will be blank. If
   it is not, enter the password you set or contact the manufacturer.)
4. Type cd system32\config and press Enter
5. Type copy SYSTEM c:\ and press Enter
6. Type exit and press Enter
7. Boot the PC back into Windows
8. Click Start > Run Type: regedit and press Enter
9. Click on HKEY_LOCAL_MACHINE (Don't expand it)
10. Click File > Load Hive...
11. Browse to and select C:\SYSTEM
12. Specify key name TEMP and click OK
13. Expand: (click the + next to) HKEY_LOCAL_MACHINE > TEMP > WPA > MedCtrUpg
14. Change the IsLegacyMCE value to 1 and click OK (notice it is the number one, not a lowercase L)
15. Click on TEMP subkey (under HKEY_LOCAL_MACHINE)
16. Click File > Unload Hive click on Confirm
17. Reboot the PC.
18. Boot into the Recovery Console using the Windows CD again
19. Select the installation to log onto (default: 1) and press
    Enter.
20. Type cd\ and press Enter
21. Type copy SYSTEM C:\WINDOWS\SYSTEM32\CONFIG\SYSTEM and press Enter (Choose yes to overwrite)
22. Type del SYSTEM and press Enter
23. Type exit and press Enter
24. Boot up Windows.
25. The Join Domain option should no longer be grayed
    out!