NetBEUI (Network BIOS Extended User Interface) is an Extension of NetBIOS (Network Basic Input Output System) ann is a seperate Network Protocol in its own right, like TCP/IP IPX/SPX and is really only suitable for small networks (it is approximatley faster than TCP/IP with 2-15 computers). If you want web-serving, then you must use TCP/IP. And you don't need 2003 Server for a File Server, do it on the 2k Box by creating a share and then you can create a mapped drive (Network Drive) on the others pointing to the network share.
You'll only need extra CAL's if your running Microsoft Terminal Services, a CAL for every client connection.
Do you want to use Windows Server? I can't see how unless you want DNS\DHCP\IIS or RAS (note: never gotten this to work
)? If your after a simple network just install XP on all of them, connect them and let the wizards do the rest.