Exchange 5.5 server

It’s well known that Exchange 2000 server is only installed on a domain model network with active directory installed.
But what if you have a workgroup with 10 machines of windows 98 and 95, and a win2k stand alone server, can I install Exhange server 5.5 on this server and use it for internal mail exchange between users of this workgroup or there must be a domain to accomplish this?