Well, I did just that, however then my installation of Ubuntu 8.10 wouldn’t correctly step the processor up/down (because it had been configured with a Celeron, which doesn’t support those things).
Well, as I found out (somewhere on the Ubuntu forums), all you have to do is add “p4_clockmod” to your running modules (edit the file “/etc/modules” and place it at the end) and then restart.
Simple as pie. I’m quite surprised at the amount of speed switching this processor does — I’ve seen it step from 2.6 GHz to 2.2 GHz all the way down to 600 and 300 MHz. Amazing, and great for energy use and cooling, too.