Basic 2003 Server install

I?m at the point with my NT 4.0 server that I am forced to upgrade to 2003 Server in order to stay compliant with various applications that require 2003 for upgrading, etc. I have fifteen XP clients on my LAN and thus far haven?t needed a domain or AD. I prefer to remain as simple as possible without introducing a domain or AD, if this is possible. I have a rudimentary understanding of AD, DNS and domains and would consider myself just above a novice in those areas.
Can anybody tell me if I must have a domain and AD in order to install 2003 Server?