As mentioned in my last blog entry I'd be adding a new feature to Aerofoil to allow automatic profile switching between Vista's "High performance" and "Power saver" power plans when you run on AC or battery respectively.
This feature was added in 1.4 beta available as an optional switch in the right click context menu - "Auto Power Plan". You must have the two aforementioned power plans for it to work - these come with the English version of Vista as standard. (Sorry no Internationalisation yet so they must be the English names - please modify the source code if you want to improve or fix this).
Whilst I've not heard of any damage occurring from switching power plans more frequently, as usual use Aerofoil at your own risk - note the program's beta status, which means it may have bugs or small memory leaks.
Final 1.4 version available here
Download Aerofoil 1.4 beta with auto power profile - possibly some small bugs (source code).
or you may prefer...
Download Aerofoil 1.3 with no auto power profile option - very stable (source code).