I'm in the process of upgrading my 15 in 1.33 GHz PB to try to eek a few more years out of it. I just replaced the 80 GB hard drive with a 160 GB, and am going to get a new battery, too, since the old one doesn't have any life in it. I currently have 1.5 GB of RAM in it. Would I see much of an improvement in performance if I replaced the 512 MB stick with a 1 GB stick, bringing the total to 2GB of memory? I know the recommendation is always to max out the memory, but I don't want to throw too much money into a 3 year old machine if it isn't going to make much of a difference in performance.