Random double entry on keyboard and mouse commands

Two mice ago and four months ago, now on my 3rd mouse, single clicks began RANDOMLY registering as double-clicks. Checked properties; drivers; changed click speed; checked out mice on other computers (ok); switched PS/2 to USB and back to PS/2; etc) the behavior remained on one computer (Asus/P4-3.0/1GB/XPproSP2). THEN the keyboard began entering random double entries on characters. So I checked keyboard properties (ok) and then replaced the keyboard (no change) so then replaced with a USB keyboard (no change). No hardware or software ADD preceded behavior. Forum on Cnet came up empty of solutions - but same behaviors were noted by others. Anyone have any ideas short of a dismantle?