I have a dual-core AMD and have always felt the performance was under par, having upgraded the memory to 4Gb fast 800Mz memory, I now know the reason! The original 2Gb memory was 566Mz and the difference has to be experienced to be believed. The system boots faster, loads programs faster and of course, with twice the memory, I'm able to keep multiple applications running without performance degradation. The Kingston has a high quality feel and installs in seconds, really simple.
In short, I upgraded the memory and avoided a CPU upgrade! Highly recommended.