Visual Basic and DirectX

Is anyone using, or know of someone else using, Visual Basic 6 or .net with DirectX and can provide any information related to the speed of fps games made using these? I''m currently considering making a fps-style educational game that requires the user to dig in the ground. Because of this I''ll be trying to mimic digging exactly. This can be very graphically intensive but since it''ll only be occurring in a small area (say 50m x 50m realworld) it may be okay. I am familiar with a VB engine using DX called TrueVision3D and I''ve seen it make terrain using a heightmap so I''d presume I''d be able to somehow modify a high-res heightmap and redraw the terrain to show the new dug holes? Another ''feature'' I''m considering implementating are features such as caves, tunnels, etc and I have *no* idea how to implement that. At least I doubt a heightmap would pull that off. Any help would be appreciated, and since I''m new to this forum if there''s a better place to post it please let me know - Ian