Hi- I am shopping for extra memory for my 17" Titanium Powerbook G4. I see vendors selling both 512mHz/ 1Ghz versions for my computer. I thought that this computer would be maxed out at 1Ghz? I have the 512 that the machine came with. Is it possible to expand it by 1Ghz MORE, for a total of 1.5 Ghz? Thanks.