Instal Small Business Server 2003 in a peer-to-peer network

I have a new server with SBS 2003 on it and do not want it to automatically make itself the primary Domain server because it has to co-exist in a peer-to-peer network (XP Machines) for a while.
In the past when I have fired up new servers (pre-installed with the OEM SBS Standard) the Microsoft install automatically sets itself up as the primary Domain server. I can not see any way of skipping the step in the setup that does this.
Do you know how to do this please?