I made a small update to the Arduino DHCP library to calculate the “seconds elapsed” field in the DHCP packet based on when the Arduino starts sending DHCP packets. This may fix some issues with using a Mac as a DHCP server. Special thanks to Arduino forum member smartperson for the suggestion.
Download here: Arduino DHCP Library v0.4
Previous Versions: v0.3, v0.2, v0.1
Additional instructions can be found on the original DHCP library post.