Nice..!
Nice work, Brian..!
I saw this ages ago, and thought I'd look it up again to see if you've updated it..
Something I noticed is that if you get to top speed, let go of 'up' and hit 'down' (reverse), the physics skips and you immediately start driving backwards ;)
If you look at the post in my profile (www.guil07.newgrounds.com) I have been developing a tank engine, and it is very similar to this! I think I emailed you awhile back but didn't get a reply =|
My next version is pretty much making the leap from an engine to a game.. You should really make a game, there's not many where the turret is separate to the tank =]
Keep up the good work!
~Guil