I dont think an orbital tool is what you need.
Just had a quick look on ebay and found this:
Its silverline which is cheap but fine for occasional use. This kit has the sponge mops which is what you need for car body work. The best compound to use with it is called Farecla G3 see here:
This 400g tube should do 1 car depending how you use it and size of the car.
My tip is get a re-usable spray bottle like you get from garden centres, fill it with water and occasionally spray the area you are compounding to stop it drying out and to keep it lubricated.
Then just wax the car to protect and bring it up shiney!