I've done this before with waypoints and it tends to look really stupid in-game. Especially if you have the vehicle ping-pong along the path because it will do a 180 degree turn in a couple milliseconds.
Another option is to animate the vehicle in 3dsMax or another 3d package that allows export of animated .x files. The animation can then be called like any other animated entity. Collision may be a bit of an issue, but it certainly
looks better. I have done this before. If I can find the test game or test map, I'll upload a video of the results.
EDIT: I couldn't find the original test game, but I still had the animated vehicle. Here's a video of the results:
.x Animated Vehicle
~Dave
Phoenix Sentry Programmer