When I bought my laptop, an eMachines M5310, I discovered that the PST tables were messed up.
What that means is that up until the kernel version 2.6.6, the frequency scaling didn't work, which meant that the laptop was running at full speed all the time and became dangerously hot. You can have a look at Dave Jone's page on the problem
Anyway, I ended up hacking a piece of code from the RTDVS project to provide a /proc interface to the frequency scaling of an AMD K7 (Athlon XP-M). It's a module that works with 2.4 and 2.6 kernels; it can mess up pretty badly your processor, solook at the README file before using it !
Here's the README
and you can find the package here
Last modified: Sat Mar 20 18:10:44 EST 2005