I bought a new iBook G4 933Mhz in February of this year, and I'm ready to upgrade my RAM. I just have the standard 256MB right now. I took a look on the Apple site and I see that there are two options. I can buy another 256MB card for $100 or a 512MB card for $200. My question is, if I spring for the 512MB card, will my laptop be able to use both it and my original 256MB card and bring my total RAM to 768MB? Or do I have to totally replace my original card with the 512MB card? I guess it all depends on whether I have one or two RAM slots, or whatever you call them. Could someone tell me, please? Thanks.