After reading many posts on memory and OSX it seems to be general opinion that you have to have 1GB+ to run this smoothly. So, I want to upgrade my 512MB macbook to a gig. Can I just put a single 1GB stick in the laptop or does it have to be in pairs? If I can just put the one 1GB in can I leave a 256MB stick in to give me more RAM? I'll probably be buying a second 1GB stick at some point, but I can't afford it right now. Is there much to gain from 2GB over 1GB? I use mainly internet, with a bit of video processing and programming. Thanks.