I am having this issue on not one, but all
four pc's - All systems have different system specs, but all are running the CPU at 100% when it should be practically idling.
My experience is the problem is drivers.
You will need to update the drivers for your Motherboards - Video - Audio on each machine from the maker of the motherboard or maker of the PC if its an HP etc.
Disconnect all external devices (USB, Firewire, Parallell, serial etc) and isolate the PC so its only the keyboard, mouse and screen connected to it.
The boot it up and see if it runs smoothly. Use performance monitor to see the CPU usage (on CPU tab) and check the list to see what is consuming the CPU usage. (My issue was system interrupts was up at .70 - .90 CPU usage and would crash the system, but also it dragged real slow as you describe).
If you still have the problem with everything disconnected, eliminate programs that use external drivers one at a time and reboot each time until you isolate the one that is causing the problem. Productivity apps like peachtree should not be a cause, but programs like GPS updating software have drivers etc.
In either case once you isolate the problem (a device or program) - find the appropriate vendor and find updated drivers/patches for windows 7 - update and reboot. Reconnect devices one at a time and monitor the CPU usage to see if there are more than thing causing it.
While this is a very painful process, it worked for me and I spent a total of 6 hours overall to troubleshoot and fix the problem on mine.
You may already know what I said above, in that case consider this a confirmation.
Hope this helps.