I recently built a new computer system with an AMD X2 64 processor. My first shot at installing an OS on it was with Ubuntu 7.04. After the initial install menu, it would just go to a black screen and not continue. So, I booted again and looked for clues in the help menu. It suggested I use noapic and nolapic. Once I put those options in, it installed without any further problems.
Once I got the OS installed, everything was working great. It's a very quick and responsive system. I know that my processor is capable of scaling back to 1 Ghz when it's not under any load. So, I added the cpu frequency scaling monitor to the panel. Right away, it told me that frequency scaling wasn't supported, and confirmed this by always showing it at 100% speed.
At first I figured that Ubuntu must not support frequency scaling. But, after booting with the same options and installing a couple other distros with the same results, I realized it was probably because of the boot options I was putting in.
At this point, all I had to do was boot only with the noapic option, and not nolapic. Frequency scaling, at least on an AMD X2 64 seems to rely on lapic. Lesson learned.