>Generally speaking, each company would be in its own database. You would open the database in that company's directory. If you have shared resources that are distributed among all the various companies, these can be in another database.

Unless using .DBF files it's not an easy approach database per company. If you use SQL Server DB best approach is add a company field for each table for separate companies. Axapta and SAP uses this approach. So you can create company based or mixed reports easly, or you can make address and person tables public, others private etc...

Axapta and SAP also have another field to separate company groups.

Of course you can't use this approach with .DBF files because of 2GB barrier.