database sharing in vista

I have 4 new dell inspiron pc and a dell printer and have network
connectivity. 2 pcs have vista business and 2 have vista home premium.

I have one pc plugged into a dsl modem and the dsl modem plugged into a hub.

I can surf web from any pc and printer is shared and database (dentrix
dental app) is shared. Each pc can access the database but after a brief
period of use (1 min to 30 minutes) subsequently crashes the database.

I am at my wits end and the dentrix support is of no use. Any assistance
would be greatly appreciated.

Thanks
chris