Paula,
I think that Intuit controls usage by limiting the use of an installation copy to one desk computer workstation and (strangely to my mind) one "notebook."
I am not certain that this will work, but it is what we were doing with Quickbooks 2006 and plan to do on Quickbooks 2009. Install a 1-user copy on each of the workstations on which you plan to use Quickbooks (not the same copy). Put the Company File on the network server, and open it from Quickbooks on the workstations. It will probably not allow both persons to update the Company File at the same time—i.e. one of them will work with a read-only copy.
There may be more to this that I don't know about.
Al Irvine, Eveoke Dance Theatre, San Diego, CA