I am assuming you are using

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.