"And, presumably, when you want to have a new car you start with a big block of steel and go from there?" plus all the wires, plastic and everything else that makes up a car!! Or from a sculpture point of view, how do you make a lump of steel, wires and plastic into a car? You chisel away everything that isn't a car. Not that a car is a sculpture and in actual fact we're not talking about cars or sculptures.
To CrossRoadLife184 I say download one of the many freely available forum packages and look at the amount of scripts needed to make it work and then maybe go get yourself a big lump of steel, some wires and some plastic and spend some time trying to craft yourself a car - it will probably be easier !!
Just google PHP forum scripts or something similar, there's loads out there and they're relatively easy to setup and customise, then crack on with that car sculpture and let me know how it goes!!!