GMAX boolean operation

Hey all. I'm trying something in GMAX I just can't get a handle on. I have a place on my Phoenix scenery where a freeway goes underground below a park and I have an excellent photoreal high-res shot I'd like to overlay on a plane above the scenery. My intent is to flatten the ground below that plane so that I can actually have the freeway angle down through that tunnel. It's a simple thing to just put a rectangular plane over the cutout area and texture the photo onto it but then the areas on the image where the freeway drops I need to exclude from the plane. I'll then texture road planes for the freeway. It'd make it easier if the road was perfectly square to the area but it angles and curves in and out. Here's what I envision but I have no idea how to make it happen. Create a plane that follows the roadway and use a boolean subtraction from the main texture plane for the cutout. It appears GMAX can do that but I can't tell within GMAX if it's working. When I apply the boolean I don't see the hole in the image. Can someone point me to help on this subject please. This would be very cool if I can get it to work.This is also posted at Scenerydesign.org.Art