Check US versus THEM’s site on Microsoft Small Business Server 2003 and Microsoft’s Technet for a Comparison of Windows Server 2003 Editions.
SBS server contains Sharepoint, has limitations but is for small business as the name implies. Web Edition is also limited. When you look at the comparisons for 2008 server you will see similar limitations
Web Edition can not be a Domain Controller in Windows 2003. SBS and Standard edition can both be a domain controller
The word “Can” should be replaced with “Must” because they must be the DC and hold the Master AD cataloug. <-I may have termed that wrong.
The point being is that they have to be the only DC on the network. The higher end editions of SBS will alow a 2nd server but it must be added as a 32 bit workgroup server.
I to run Forest run as far and as fast as you can from anything with the SBS tag on it. Microsoft just rips too much stuff out of the system to make it useable in a evolving enviorment like a small but growing business.