The freeware system utility CCleaner has dramatically improved system responsiveness and overall performance for a couple of desktop PCs that I administer. I saw the option to clean “Old Prefetch data” under the Advanced menu. According to this link, there is never a need to clean Windows’ prefetch data, and in fact, doing so will temporarily reduce system performance.

http://www.populartechnology.net/2005/10/ccleaner-cripples-application-load.html