Sorry, you can't replace the CPU---nor can you replace or swap the entire logic board (motherboard). However, if it makes you feel any better, I have one of the first MBP (1.83 Core Duo 128 graphics card 2 GB RAM) and a recent 2.4 MBP (Santa Rosa, 64-bit, 256 graphics card 2 GB RAM)---because of my work, they sit side-by-side in front of me running the same or similar applications all day long. I don't actually notice any difference in performance. I know that if you benchmark test them or time them in running something, the new one will win (not by much), but in day-to-day typical video, photo, word processing tasks, one does not perceptually stand out over the other.
You've got a fast computer, enjoy 😉