Leggendo i Software requirements relativi all'Operating system per l'installazione stand alone di WSS 3.0 dal seguente sembrerebbe che sia possibile anche usare Windows Server 2003 Web Edition a patto il Windows Internal Database
http://technet2.microsoft.com/windowsserver/WSS/en/library/700c3d60-f394-4ca9-a6d8-ab597fc3c31b1033.mspx?mfr=true
Windows SharePoint Services 3.0 runs on Windows Server 2003 with SP1 or later. We recommend that you apply all critical updates. You can use the following Windows Server 2003 editions:
Because of Windows licensing restrictions, if you are using Windows Server 2003, Web Edition in a single server environment, you can only perform a Basic installation. This is because the full SQL Server editions cannot be installed on Windows Server 2003, Web Edition. However, the Windows Internal Database can be installed.
In realtà il setup quando viene eseguito su W2003 web edition non installa il Windows Internal Database e come riportato dal seguente su tale sistema operativo è solo possibile usare WSS come front-end.
http://www.microsoft.com/windowsserver2003/howtobuy/licensing/sharepoint.mspx
Windows SharePoint Services conforms to the Windows Server 2003 licensing model.
The usage of the Windows SharePoint Services on Windows Server 2003 Web Edition, is limited to front-end Web serving tasks. The data storage portion of Windows SharePoint Services may not be installed or used on Windows Server 2003 Web Edition.