OpenEdge can be installed in a servant with the projects and to give connection to several programmers
As to install the OpenEdge Architect to have it in a server Windows 2003 and the programmers having Windows XP connects him and thus to be all the project in a computer.
Probably the best way, and one of the safest to make sure code doesn't get overwritten by each programmer, would be to look at using a form of SCM (SubVersion, CVS, or Roundtable). This allows the central repository to be held on the server and each programmer then has a local copy on their pc to which they can check code in and out from the server.