Hop into the vehicle and drive over the lights quickly to activate them- this will move a platform into place in the far side of the room. Grapple up to the right, go back into the hall and get a Stormtrooper helmet at the dispenser, then re- enter this room, grapple across to the left platform and move to the back. Use the Stormtrooper checkpoint to open the door ahead.
Now then, Jabba's Palace- I'm thinking you maybe missed a bounty hunter helmet dispenser down a side tunnel to the left. This should let you activate the door mechanism to get through the gate in the Main hall. If this isn't the right section let me know and try to give a bit more detail as to how far into the level you are.