Sure. It's easy and keeps you working when you can't lug around a PowerMac and monitor. You can do everything on your PowerBook except burn the actual DVD (unless you buy one of the new PowerBooks with the superdrive). The big advantages for the PowerMac are processor speed and RAM.
Logging, importing, editing, building the DVD all take the same time on the PB as the PM. The big differences are in rt effects, rendering and encoding.