The low-powered system I assembled recently is based on a Via Epia board and a C7 CPU. I spent quite a bit of time when I was setting it up trying to get the C7's speed stepping to work. I loaded a number of cpufreq modules without luck; crawling around on the Web only led me to discussions about how the C7 couldn't be speed-stepped in Linux and maybe the centrino cpufreq driver would work.
Well, yesterday I randomly searched again -- and poof! There was a discussion from early January about how maybe the ACPI cpufreq driver would work. I loaded it, set up powernowd, and was rewarded with
daniel@jeeves:~$ cat /proc/cpuinfo processor : 0 vendor_id : CentaurHauls cpu family : 6 model : 10 model name : VIA Esther processor 1200MHz stepping : 9 cpu MHz : 400.000
Sweet. Now all I need is for the Debian kernel folks to package a version with a vt1211 lmsensors driver so I can shut down or slow the fans, and I'll be all set. (I could probably hack it in myself, but according to what I've read on the Web, the next kernel release will have a working driver)
[UPDATE: I disabled cpufreq after only a day or so, because Linux got horribly crashy with CPU scaling turned on. Hopefully the kernel will be fixed sometime in the future ]