Yes, this is the set-up that I use.
Install two sound cards to your system. Under "Sounds and Audio Devices" in Windows "Control Panel," select the "Audio" tab. Under the "Sound Playback" option, select the card that you want to use for your system sounds. Also, make sure that your speakers are connected to the correct card.
Connect the sound card that you want to play the hold messages to your MOH adapter or PBX system. In the IMS program, select "Settings." Under "Sound Out Device," select the card that you connected to your MOH adapter or PBX.
That's it! All system sounds will now be routed to your speakers and the hold messages will play independantly into your MOH adapter or PBX system.
Hope this helps,
Jared