Preventative maintaince schedule

Our network consists of 150 clients running a conglamoration of windows 95 and 98. We have both NT and Novell servers on the network. Recently we purchased ZEN works for Novell and have not gotten it totally functional yet. I would like to build a preventative maintaince schedule for all of the clients on the network to ensure that they all have the most currents BIOS and software patches. Does anyone have a solution to this that would make the process somewhat automated?

Thank you in advance