ok im on the little go cart tanks, and i beat my way trough to the huge machine, i start shooting the t-900 or what ever they are, and i dont know what to do!!

There are towers that provide power all over the area, what you do to keep the t900 count down is you shoot the towers with the secondary fire, the large cannon. Some towers are hidden behind builings, as long as you shoot all of them, and get to this point varyly quickly, you should be able to beat the level.