1.  Windows Server 2003 is available in the following editions:
 Web Edition (WE):
This version of Windows Server 2003 is optimized to host web sites
using IIS and is therefore limited in its support of hardware and in its
feature set. restricts Internet Connection Sharing, network bridging,
and Terminal Services (although you can still use the XP-like
Remote Desktop feature for Remote Administration), WE can be a
member server of a domain, but it cannot be an Active Directory
domain controller.

2.  Standard Edition (SE) :-
 This version of Windows most corporations likely will deploy.
Included with it is support for up to two processors and 4GB of
memory. SE includes most of the features and support of the other
editions, including the .NET Framework, IIS 6, Active Directory, the
distributed and encrypting filesystems, and various management
tools. You also receive Network Load Balancing and a simple Post
Office Protocol 3 (POP3) server which, coupled with the existing
Simple Mail Transfer Protocol (SMTP) server bundled with IIS, can
turn your Windows Server 2003 machine into an Internet mail
server.

3.  Enterprise Edition (EE) :-
 Aimed squarely at more demanding environments, EE adds high-
level memory management features, and some session
management features for Terminal Services. It also includes
support for eight-node clustering and booting directly from a SAN.
Plus, you can add memory to EE while the system is running,
without needing to reboot

4.  Datacenter Edition (DE) :-
This performance- and scalability-enhanced Windows Server 2003
edition supports from 8 to 32 processors and features 64GB of
memory and from two to eight node clusters. With the exception of
more extensive firewalling features, DE is identical to EE.