If you had access to the C2K server, there would be a log there which you could check by referencing the time of the print out. However, us plebs are a security risk and are lucky they dont install electrical fencing around the servers just incase we touch them.
Other than that, you can monitor the print queue by opening Printers and Faxes and select the printer and choosing 'see whats printing' from the left hand menu. It only shows print jobs currently processing and jobs in line though so you would need to be on the ball to catch the offender red handed ( and still, you would have no proof unless you took a screenshot of the print job in the queue).
