Notebook gaming: How can I lower CPU usage?

Okay, this is the notebook I have:
http://www.compusa.com/applications/SearchTools/item-details.asp?EdpNo=5020325&CatId=4942

-1.4GHz Intel Core 2 Solo ULV SU3500 processor
-11.6-inch HD widescreen
-2GB of DDR2 Dual-Channel 667MHz memory
-250GB 5400RPM SATA HDD
x64

But instead of the stock vista, I have windows 7 Ultimate. On idle, my cpu is 5–10%, and for internet surfing it stays around 20–30%. But usually, when i click to open a program or file, the cpu flashes 100%, and fluctuates between 60–80% before settling back down to the lower levels.

Its the only computer I got and I really feel like gaming, and so lately I’ve been installing old time rpgs like Diablo 2, and Baldurs gate 1 and 2 (Baldurs Gate tutu right now).

Baldurs gate 2 has good performance, but when i check the cpu usage during game play it doesn´t budge from 100%. Its a constant 100% and during gameplay my mouse icon flickers once in a while. Game speed is fine, the game seems to play well, but knowing that my CPU is at a solid 100% really bugs me, and thats with GAME BOOSTER stopping many of the background processes.

So the question- How can I lower my cpu usage for such simple old time games?

I´ve done the following:
– used programs like Ccleaner and Utilities 2011 to completely clean and care for my computer.
– Disabled Aero and most of the visual features of windows.
– Used Game booster
– cleaned the Desktop
– Uninstalled many useless programs
-defragmented Harddrive

Should I downgrade from windows ultimate somehow? And if so, whats the best OS?

I still don’t believe the problem is my processor, simply because these games are so old!