What methods are available to take stock of software inventory on a network

First time poster here so plz bear with me if this has been asked before. I have recently completed my MCITP studies and have got some work experience at a computer animation school. The school principal has asked for a physical inventory of the schools IT equipment. (3 servers, 10 admin (incl: tutors) and approx 90 students) I have completed that task.
However the school principal also wants an inventory of all software installed on PCs (excl: servers) This could be an administrative nightmare. Is there a quick fix for finding out this info or will it involve me doing the pencil and paper at each and every student and staff PC?