I wrote about how I went about setting up my new Soekris net5501:
I recently purchased a new Soekris net5501 to replace my beige box firewall. I had previously set up a net4501 but I wasn't happy with it and sold it to a friend. Large file transfers would grind it to a halt and the performance wasn't as good as my beige box. The net5501 has increased horsepower (faster processor, more memory) and a better network chipset (vr(4)). And, most of all, because there are 4 network ports! At my house I have 3 network + my FiOS connection. I have my internal LAN (wired with full access to everything), my wireless network (requires authentication and has limited access to the LAN) and my DMZ (for my web server; no access to the LAN or wireless networks).
For my installation, I use Yaifo so I don't have to deal with a serial console or setting up pxeboot. (I actually did hook up a serial console to update the bios, which I'll discuss later). Also, I use a custom rc and a flashdist-like system so I can mount my CF read-only. My "fdlite" script doesn't rely on a customized install like flashdist. It does use some of the device modifications Chris uses to make the read-only / work properly, though.
Read more at The OpenBSD Journal.