If you are running Vista or Windows 7, then you CAN kill just the sound from Trainz. This is how to do it:
When Trainz starts, hit the "Windows" key and let Trainz minimize to the taskbar. Go over to the little volume icon in the notification area and click it. The small dialog box with the volume control on it has a little blue link at the bottom for "Mixer". Click that.
The dialog box that opens lists all the applications that are using the sound card - one of them will be Trainz. Click the little speaker below the volume bar and JUST THAT program will be muted.
Bill