Click "Add or Remove A Role" to launch the Configure Your Server Wizard. If you're going to add a role, you'll need to have the Windows Server 2003 installation disk to hand. After a brief scan for network connections, the wizard allows you to choose from the following roles (may vary by server edition):
File Server - The File Server allows centralized access to files and folders based on individuals, departments, or whole enterprises. Selecting to add this role will allow the admin to manage user disk space quotas or enable indexing on the file system.
Print Server - This server role allows centralized access to printers by "serving" shared printers and their drivers to client PCs on the network. If you select this role, the Add Printer Wizard will launch and guide you through the process of installing printers and Windows print drivers. This includes, if it isn't already installed, IIS 6, and configures the Internet Printing Protocol allowing Web-based printer administration.
Application Server - This server role lays the infrastructure needed to support Web application hosting. Installing this role will also install IIS 6, Microsoft ASP.NET and COM+.
Mail Server - Selecting the Mail Server role installs the Post Office Protocol v3 (POP3) along with Simple Mail Transfer Protocol (SMTP) which allows the server to function as both an incoming and outgoing email server for clients on the network.
Terminal Server - Terminal Server allows clients on the network to access applications installed on the server, as well as server resources acting as if the application were, instead, installed and running on their own computer. Several users can use Terminal Services for the same application at a time. Users connect either through the Terminal Service client or Remote Desktop.
Remote Access and Virtual Private Network (VPN) Server - Selecting the Remote Access and VPN Server, installs the routing and remote access services for dial-in, LAN, and WAN connections. VPN connections allow remote users (or entire sites) to connect to the server securely via the Internet.
Domain Controller - Selecting this server role starts the Active Directory Installation Wizard, which configures the server you're running the installation on to function as a domain controller for either a new, or already existing domain. It will also install everything needed for directory services for network clients, as well as the DNS service (assuming a DNS server is not already present).
Domain Name Service (DNS) - Selecting the DNS server role installs the MS DNS Service and launches the Configure a DNS Server Wizard, which walks you through the process of setting up the server as a DNS server for the network.
DHCP Server - The DHCP (Dynamic Host Configuration Protocol) Service provides automatic IP addressing to clients on the network that are configured to obtain dynamic IP addresses. After choosing this role the New Scope Wizard runs, allowing you to define at least one IP address "scope", or range, for the network.
Streaming Media Server - Selecting this server role installs Windows Media Services (WMS), allowing the server to stream multimedia (music, video, etc.) content over an Internet / Intranet connection. Content is considered "on demand" and delivered in real time.
WINS Server - The WINS service is only needed to support older operating systems like Windows 95 or NT, which use NetBIOS name resolution. Choosing this role installs the WINS service which provides computer name resolution, translating NetBIOS names into IP addresses.
The process for installing each individual server role is unique, and may require you to have various pieces of information on-hand. If you're installing the DHCP service, you need to have already decided on a IP address scope for clients. If you're installing the Domain Controller service, you need to be sure you already know how the network as a whole is or will be configured. I suggest you read up on the installation steps for each server role prior to beginning the installation and configuration.