We'll use rollers too. I like the wood dowel ideas -- agree they've got better surface friction and are less breakable, but we want to do some special surface and handling tricks that will be better with PVC pipe. To attach a drive, drill a hole in the center of an end cap, and place a screw of the right diameter (1/4" or 3/8", depending on the specific purpose of the roller) through the hole, then secure it with a washer, lock washer and nut -- and also some epoxy on the screw head (inside the end cap). Then glue the end cap on the roller/pipe. Can then place either a hub, sprocket or motor drive attachment/coupling directly on the screw. We plan to build several roller assemblies, and drive them all from a common shaft going through the base of the robot -- with drive sprockets attached where necessary.
Good luck!
