Microsoft Small Business Server is an ideal server/domain solution for the small business. The latest version is SBS 2003 R2. It includes Windows Server 2003 R2 (server, active directory, IIS, etc), Exchange (mail), ISA (proxy & firewall), WSUS (patch management) and Sharepoint (web based collaboration).
A new step by step document has been released by Microsoft to guide you through an installation of SBS 2003 R2, including upgrades from previous versions.