I'm interested in buying a Powerbook G4 (1.5GHZ, 512MB of 1 SO-DIMM RAM). If in the future I required more RAM, say... another 512MB 1 SO-DIMM upgrade, would that be possible? I'm really clueless in regards to the Powerbook's hardware architecture, so any information on how to save money instead of using Apple to upgrade RAM (ridiculously expensive) would be appreciated.