Well, I now have a version of the Arduino DHCP library that I feel moderately comfortable releasing to the wild. If you're interested in the background story, check out these posts.

Download here: Arduino DHCP Library v0.1

I've tested it with an Arduino Duemilanove (ATMega168), but I'm positive that there will be bugs in the code and that for some (hopefully not many) people it will just plain not work. If you do try to use it and find that it doesn't work, try using Wireshark to see what packets (if any) are flying across the wire. Even if you can't figure it out, sending Wireshark capture logs to me will be helpful for me to debug.