I am trying to remember a very old and cool game from pre-2000 or around that time.
This games have vehicles, and you're controlling the vehicles. Multiple vehicles ranging from small to big, I think you start out as the small ones. Vehicles can 'jump/float' and carry weapons. Killing enemy vehicles can give you access to maybe money and sometime, pickup their weapon.

The game appear to have a 3d overhead world, maybe slightly slanted camera angle. Some wood/hill setting I guess, organic feeling. I think there were bugs you can squish for money or something. I think, the vehicles might actually be tiny compare to the world.

Basically, the game feature jumping cars that can shoot other cars, take their weapon and money, crush some bugs for money..etc
I would like to remember this game if anyone understand what I am describing...

Seems like some Micro Machines knock-off, how 'bout Motor Mash then?

Also sounds like Vangers maybe?

Vangers is what I thought of too; though when I tried the demo, back when it was released, I didn't get to play for very long before it blue-screened. There are some relevant links on the Wishlist page: http://www.gog.com/wishlist/games/vangers