Multiple LAN solutions for a small office. Is a server VITAL? 1

[Drkhrt]

I have three small companies in a "small" office.
One I want to peer to peer network (only 2 users) BUT I want one of them to be able to access the other two LANs. One LAN needs to share files between 10 users and the other LAN has 15 users. I am being told it greatly increases the maintenace / downtime to use one workstation as a server (one per LAN) and a seperate server for each LAN is vital, or at minimum one server for both LANs. I don't want the companies to have access to each others files. Is he just trying to sell me a server or do "you" have a suggestion?

 

[Kjonnnn]

What about having ONE server with separate partitions for each of your company. You would have to maintain the one server, but make the partitions NOT shared among the 3 companies.