Since you have a 2008 server available on the network, have you considered moving the DHCP Server service role, to the 2008 Server machine, I know it's not the solution, you're looking for and possibly not a solution at all, just an option. I know that we've seen and discussed issues with Windows 7 communications with a 2003 server, being used as a print server and the issues seemed to revolve around something relatively new from Microsoft called, "Asynchronous RPC"
you can google it and maybe get some understanding, but basically it's intended to speed up communications between Windows 7 clients and 2008 and 2008r2 servers. That particular issue for that member was to move his print server to a 2008 server on his network and the problem disappeared. Again not sure that this is an issue in your specfic case, just thought I might throw it out there for your consideration.