The extension-device mapping is read from the following registry key (XP):
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\MCI Extensions
The device-DLL mapping is read from the following registry key (XP):
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\MCI32
The value "MpegVideoOld" comes from your registry: apparently some installation has renamed what has been "MpegVideo" before.
HTH, can't do any thing without more information,
Donald