I had a thread before where I said that my computer ran hotter with Vista 64-bit. I've figured out why that is. I'm on a laptop and my processor is always at 2000Mhz, even when I'm idol. The processor used to run at 800Mhz with 32-bit while idol. Why does my speed step not work? My two core loads always seems to total at least 100%, even on idol. I don't know why this is. The only new thing is that I now have 64-bit.
Well my Vista 64 bit laptop is running at 798 mhz, so it's working here. When you reinstalled you may have altered the power options back to a default of 'high performance'. There should be a 'power options' icon in your system tray, set it to 'power saver' or 'balanced. and the CPU speed should throttle back.