I was starting to make GTA2 mod for CS2D, I have almost all GTA2 car images, and start script. I even said about it somwhere, now I don't see. What GTA exactly will you do? based on GTA 1,2,3, VC, or SA?
I think i can help you with my carmod.
When i finish first my BF2D mod. It's cool, but it have some problems with lag. Another thing, you should make a vehicle menu. or jetpacks etc..