Yes, there is a write up for the process! http://h10032.www1.hp.com/ctg/Manual/c00444840.pdf It requires removal or the optical drive, hard drive, keyboard, monitor, and some plastics, but it's easy if you've ever worked on a computer before. That guide from HP is very good, except there are an additional 7 screws you need to remove from the plastic base it doesn't tell you about.
Also, I found a program called RMClock that I've used to further lower CPU power consumption. CPU now idles at .85v and full power at 1.15v (vs 1.0v and 1.3v default) RMClock should work with the Sempron too.