I am assuming you are using the concurrent session hack? If so, the easy route is to use a different user account but I realize this isn’t convenient for everyone so…
What you need to do is:
1- Depending how you launch Media Center currently, prevent it from starting by deleting the corresponding registry key from the branch below.
[HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun]
2- Create a batch file to conditionally launch Media Center. Something like the below would work.
@ECHO OFF
REM If we are not the Console session exit now
IF NOT "%SESSIONNAME%"=="Console" EXIT /B
REM Launch Media Center via Shell
START %SystemRoot%ehomeehshell.exe /nostartupanimation
3- Optionally create a VBScript script to launched the above with a hidden window (Note: I know I could do it all in VBScript but some people may not want this route)
Option Explicit
Dim shell: Set shell = WScript.CreateObject("WSCript.Shell")
Call shell.Run("LaunchMediaCenterOnConsoleSession.cmd", 0, false)
Set shell = Nothing
Note: Replace LaunchMediaCenterOnConsoleSession.cmd with the name of the batch file you created in step #2.
4- Save both files in a folder of your choice. I have a folder called bin on my system drive I stick stuff like this into.
5- Add the script (or batch if you choose to not create create a script) to your startup. You can do that by either adding it to the HKCU Run location mentioned in step #1 or by adding a shortcut in the Start Menu > All Programs > Startup folder. Whatever you think is easier.
Attached are samples of each file.