According to what I’ve read from Microsoft…you should <i>not</i> set up access to PST files on a network drive! I’ve seen this work at times, but at other times cause some corruption…so…beware!
As was mentioned, you could look into Exchange ($$$), or even Zimbra, or open-Xchange for your needs.
I would firstly recommend Exchange as this will handle it for you..
But there are other ways. Set up a standard netword drive that everyone can see with a persistant drive letter.
Say M: and store peoples PST files on the M: drive. In peoples computer profiles you can configure Outlook to use the M:person.pst or somesuch as the path to their outlook folder. I’ve set this up a few times and it works well.