I found something pretty intriguing and wonder if you have also noticed this on your system (for those with Vista/XP dual system).
I am using Everest Ultimate to monitor the temps on my PC in both Vista and XP. I was surprised to see that the CPU and HD temps are 3 to 4C lower in Vista than in XP, and 1 to 2C lower for the GPU and board temps.
CPU Vista: 40/41C
CPU XP: 44/46
HD Vista: 30/31C
HD XP: 36C
GPU Vista: 40/41C
GPU XP: 43C
Board Vista: 40C
Board XP: 43C
Looks like Vista was kind of optimized concerning power consumption/temps etc... all in one it's pretty good indeed
Oh and it's pretty cool Everest Ultimate 2007 comes with a vista toolbar gadget so you can have your temps/voltage etc... right there