Well had a Soekris NET4801 for a longtime initially i build the image on a old machine that i discarded for many years ago, i did a quick search on the net for some interesting links about PXE booting the Soekris
i Found the following sites of interest:
Used this guide for the basic setup of the DHCP and TFTP Server and Config of the PXElinux.conf:
Setup ad DHCP and a PXE Boot server
if you need a little more reading this page will give som ideas to:
Install Ubuntu over PXE netboot (headless using serial terminal) on a Soekris Net4801
The NET4801 is not that fast and it will take some time to install the system, my system is only based on a compact flash card.