i've got a 15" powerbook that's about 3.5 years old (1GB RAM, 1.5ghz, 80GB) and i'm thinking of replacing it with a macbook. my battery doesn't hold charge well anymore, i'd like to put in more RAM, and i'm probably going to have to get an external hard drive soon - basically i added these costs up and they're reasonably substantial, and i think i'd probably be best served to just buy a new laptop instead of "fixing" the current problems. i've used friends' macbooks and i like them well enough, though i haven't spent all that much time with them. i guess my question is this: will i see any step-down in performance in going from the powerbook to a macbook? getting the macbook pro isn't a possibility because of budget constraints (i'm a grad student) and i don't do any major sound/video editing that'd really take advantage of the pro anyway. so, does anyone have any suggestions?