Well I tried to look at the problem from a bigger perspective. I decided to use a plane a normal plane defined in 3d space. Then I took the surface normal of this plane and then determined the amount of rotation to get from my perspective normal angles of x,y, and z axis. This took me almost a week just because I really had to study back up on vector and matrix multiplication, dot and cross products. I actually now have a tank that follows the terrain :) I am way more then excited as I was almost ready to give up again, on a game project. What usually happens is I get to a point I get stuck at, but my partner, my son, helped me with the special type of motivation he does.
I'm going to get some screen shots and also get some videos for everyone to see. I'm more then excited about this as this was a major sticking point. But see what you can do with a little ingeniuty and determination? Also sorry about the lack of updates you know Battlefield 2 came out. And I was going to check on my World of Warcraft guild and got a damn authentication error again.
Also you can actually view a DivX version of the tank tracking the terrain here. It weighs in at 6.5M.