One of the quickest and easiest ways to save quite a bit of money on your network is to utilize a Suse Linux Enterprise Server (or any other GNU/Linux Server) as a Domain Controller for Windows Clients.
Microsoft not only charges a premium for their Server Software, they also charge you a “License” for every client that accesses a Windows server over a network. These licenses are called “Client Access Licenses” or CALs and are different than the License that you need to run Windows. As of this writing a CAL for Windows 2003 Server from Microsoft costs between $40 – $50 per device depending upon how many CALs you purchase. For instance, if you go with a Windows Server and you have 100 clients connecting to your server, not only do you have to spend the thousand(s) of dollars for their server software, you would also have to spend an additional $4,000 – $5,000 just on Client Access Licenses.