CPU-time limit control

Hi, We have a quad Opteron server with 32GB RAM running SuSE9.1, the server will be used by many users running application softwares. In order to better manage the computing resource, we want our users to submit their jobs to one of the OpenPBS queues. I wonder if there is a command/script or system tool I can use to limit the cpu time for all processes running in interactive mode? Regards Jyh-Shyong Ho, Ph.D. Research Scientist National Center for High Perfprmance Computing Hsinchu, Taiwan, ROC