Peer-to-Peer “Sharing” of “PST” Files

Existing setup of Outlook: four users on a PtoP net, each on running Outlook2000 with a local PST file and each one “sharing” their local directory containing their PST file. Each user then has a folders branch of their co-workers entire email stuff. Suddenly, only ONE user at a time can access Outlook… Does anyone have any experience in such a crazy setup & is it possible that the combined size of the users’ PST files as reached some limit? Any help???