I think CoolBook effectively has the same functionality as VoodooPower, but geared less towards throttling/multipliers and such. You just set the frequency and then lower the voltage as low as you can while maintaining stability. It's a different approach and the documentation is fairly interesting, actually. For me at least, this was very difficult to figure out using VoodooPower, and VoodooPower didn't have the capacity for undervolting until relatively recently anyways.

You should definitely only have one of VoodooPower or CoolBook running simultaneously. I believe that CoolBook will run on anything that has some sort of Apple notebook model identifier (e.g. MacBookPro4,1 or something), which can be changed fairly easily. Also you should be aware that you have limited activations of CoolBook (only two I think). This isn't much of a problem because it survives updates and restores from Time Machine, but if you do a clean install you'd probably have to reactivate.