Jordan Terrell sent in this link to a DHCP library he’s been writing for Arduino Ethernet. It’s part of a larger RFID door lock project he’s working on.

I knew that the Arduino Ethernet hardware and supporting library didn’t directly support getting an IP address (and other supporting information) via DHCP. I began to look around to see if someone had developed a library that would handle the DHCP handshake, and unfortunately I could find no such library – only comments of people wishing someone would develop such a library. Well, I’ve started just that – a DHCP library for the Arduino Ethernet shield.

DHCP Library v0.1