J.,
I have 5 boys and for years we have been makeing their cakes at home. It really isnt that hard. We have made an articlated tractor, a bulldozer, a drag line crane, a pick-up truck, a school bus, a tug boat, a train, and quite a few more.
We use the cut up cake method. For the pick-up truck which was probobly the easiest we used 2 loaf cakes (just bake the cake in a loaf pan) When the cakes are baked and cooled then slice the tops off to make them flat. Put the cut side of one loaf cake facing down, then cut the second loaf cake into thirds, use frosting as glue and put the 1/3rd of the loaf sort of centerd on the whole loaf. This creates the cab of the truck. You want the hood of the truck in front, and the bed of the truck behind the cab so you would want to make that a little longer so don't center it exactly.
To decorate we always let the kids help, that way it didn't have to look perfect. We used graham crackers cut in half lengthwise to form the sides of the bed of the pickup truck, we used small stick pretzils pushed into the cake to hold the crackers in place, but you could use wooden skewerst too. We used a long skinny tootsie roll for the exhaust, and sticks of gum for the windows. Then we filled the bed of the truck up with candy corn one time, and another time we made it we filled it up with bite size shredded wheat cereal. The wheels were small chocolate donuts.
You are only limited by your imaginition, and once you get the hang of doing it your ideas will go off in lots of directions. If you have any questions email me.