I previously used a Winform app that was a simple DHCP service to assign addresses on a closed LAN network for test servers. It was unreliable, in that it would assign addresses but would never let the lease go beyond 15 minutes or so.

I just replaced it with Open DHCP Server. If you are looking for a simple DHCP server, try this one: it is on SourceForge.net. It installs on Windows as a service, and uses an easy to configure ini file (with lots of comments). I like that I can assign addresses with an infinite lease. It also has a web interface on port 6789 which shows the active addresses.

A very simple and well written piece of software. The project is located here.