I finally updated my DHCP Option Code Utility to make it compatible with Mountain Lion. This gets round a change Apple introduced (it had worked fine with Tiger, Leopard, Snow Leopard and Lion).
DHCP Option Code Utility makes it easy for mere mortals to generate the encoded values needed to define DHCP Option Codes for use with Apple's DHCP server. The most common uses of DHCP Option Codes are to define extra fields of information to advertise things like a VoIP phone system or a PXE Boot Server.
I also took the opportunity to add the ability to define 'null-terminate strings' as well as normal strings.
More details along with a download link can be found here.
[As a belated update to this post - I did sometime ago confirm that version 1.1 also works fine running in Mavericks, and that the DHCP server in Mavericks Server.app still accepts the same encoded values. Version 1.1 can therefore run on 10.4 all the way up to (currently) 10.9.2 and the values work with 10.5 Server through to Mavericks Server.app]