Sorry all - but for powerbook, only one way:
Brenthaven Powerbook backpack... expensive, you bet. But indestructable, with compartment sized for your size PB. Plus waterproof, convenient, and frankly a nice feature: understaed. But yes, E X P E N S I V E. Oh, I'd buy it again in a heartbeat.
Check it out in person @ Apple store or some Comp USA's... then go buy it somehwere else (they want list price)
Peet