Replying to Update G4 powerbook, or get Macbook pro?

Alright I am starting to take my music production work more seriously now. Should I upgrade my powerbook g4 by adding my memory and a bigger internal harddrive, or should I just save up money for a macbook pro? and no, I will not go PC, apple it is.

I have a 867 MHZ powerpc G4 processor and 640 MB of SDRAM , my harddrive is 50 gig internal but i have a 260 gig external.

What do you guys think. Will my computer be able to run multiple programs at once?