AppleShare Print Server (2.x, 3.x, 4.x, and AppleShare Pro) don't provide the option to automatically reprioritize print jobs. That is, you cannot configure the spooler to automatically give some clients' print jobs a higher priority than other clients'. You can select any print job appearing in the print queue and request it print next, and you can cancel print jobs higher in the queue while that job is being received or sent by the spooler. After the spooler has shipped the print job off to the printer it no longer appears in the spooler queue and cannot be canceled.
You may wish to investigate other high-end spoolers such as Print Central by Compumation Inc. and Novell Netware which enable you to reprioritize print jobs. To locate a vendor's address and phone number, use the vendor name as a search string.
Below for your convenience is the Redgate reference on Print Central:
Print Central
Print Central is an easy-to-use print server for the processing of high volumes of print jobs to PostScript output equipment. It offers the advantage of a "multiple device" print server so a user's computer is released instantly while Print Central handles the downloading of jobs to the printer(s). This multiple printer queue capability provides the simultaneous spooling of jobs to many print devices over a network. Print Central gives users a greater level of productivity by reducing the amount of waiting time that is often associated with the printing of large or complex files. A network administrator can perform management functions, such as reprioritizing, removing or putting jobs on hold remotely from their workstation. Print Central provides up-to-the-minute error and activity reports, giving an administrator complete information about the status of jobs and the amount of traffic on the system.