The DirectX SDK is a collection of libraries, documentation, media, and some example/tutorial projects. There's nothing really that uses a whole lot of CPU resources unless you happen to be running the example projects at the same time as your game (which I doubt).
These programs clean the registry, you might try one of them:
McAfee Antivirus
Norton Antivirus
Windows Live Onecare
Registry Cleaner
All of those have free trials, if not are free (in the case of the last one). Good luck!
"...The Protoss do not run from their enemies. Aiur is our homeworld, it is here that we shall make our stand!" -Aldaris