Cleaning hard drive
How do you clean unwanted cookies, etc from the hard drive that might be impeding performance?
iMac
Open the Finder. From the Finder menu bar click Go > Go to Folder
Type this exactly as you see it here:
~/Library/Ccookies
Click Go
Move the Cookies.plist (or Cookies.binarycookies) file from the Cookies folder to the Trash.
Doubtful that just deleting cookies would have much affect on the performance of the hard drive.
Avoid third party "cleaning' utilities as they can do more harm than good. Your Mac runs maintenance for you > Mac OS X: About background maintenance tasks
Make sure there's enough free space on the startup disk. Double click the MacintoshHD icon on your Desktop then click Get Info. You'll see Capacity & Available. Make sure there's a minimum of 15% free disk space.
For Mac OS X 10.4, 10.5, and 10.6 > Mac maintenance Quick Assist