Set the Plays ("Play Count" before iTunes v9.2) of the selected tracks to a user-entered number (they will all be set to the same number). If this number is 0 then the Last Played date of each track will be erased. (iTunes has the ability to "Reset Plays" to 0 from a track's contextual menu.)
Also see Add or Subtract Play Count.
Perhaps Also of Interest...
downloaded 2m 29s ago
Applet assists with swapping, copying, appending data between track tags
downloaded 9m 33s ago
Renumber order of selected tracks
downloaded 13m 36s ago
Convert or import tracks with any encoder on the fly
downloaded 22m 27s ago
Convert selected tracks and export the converted files to a new folder
downloaded 41m 23s ago
Swap the name with the artist of selected tracks
downloaded 43m 40s ago
Parse Song Names and reassign the parts to other tags