What did you use for making the mesh? The way I exported collision meshes for ramps was the following:
(NB.: I'm using Blender 2.49b with the 0.97b3 version of the dts exporter)
-Make the mesh - it has to be a convex shape! If you want something concave, make it from two convex shapes!
Setting up the exporter :
-Change the detail level to "Collision"
-Make the button correspond with the layer where the collision object is found
-Export