I looked into it for my Aspire 5020 (5021). The long and short of it seems to be:
1. Maybe: but it's not very easy, as there's no simple or uniform way to do it. There are a few patches floating about to do this (lots for the Centrino's lately), but I couldn't find much for K8 (Opteron/ Athlon 64/ Turion 64), only K7 (Athlon).
2. What I've come across so far suggests the machines are far less stable with Linux than Windows when you start cranking down the voltage, but YMMV.
To be honest, I gave up after looking into this for a while, so good luck if you get any further than I.