There are a number of interesting tutorials out there on making track dollys, stabilizers, jibs, booms and cranes for camcorders and cameras.

Here is a suggested list of sites :

John Beale - Making a Camcorder Stabilizer

John Beale - Camera Jib Arm

Ron Dexter's page photos of do-it-yourself skateboard-wheel dolly ideas

Paul Turner's boom made from a parking sign

homebuiltstabilizers has many impressive cranes, dollies, and stabilizers

Skateboard Dolly (original page gone, this is an archive.org mirror)

Johnny Chung Lee - Why build a cheap steadycam

Do-It-Yourself Stabilizer for the XL-1