Your main problem right now is memeory so I would go that route first. My girlfriend is still holding on to her 1000mhz Celeron mobile laptop. It was painfully slow as it only had 128mb memory until I upraged it to 384mb. Now it handles music and everything except a few video files fine.
If you get your memory maxed out it should solve your performance problems, I can't imagine CD changer software taking a lot of CPU power to reqire a processor upgrade. Also while upgrading RAM on laptops is fairly simple, things get a lot more complex when you want to get to the CPU.
