JANET, the Uk's Education and Research Network, provides a sample AUP that offers useful examples of acceptable and unacceptable behaviours. This can be accessed here: http://www.ja.net/company/policies/aup.html.
JANET have also produced an informative factsheet on Dealing with Computer Crime. This is available here: http://www.ja.net/documents/publications/factsheets/018-computer-crime.pdf.