Before trying the NIC card option, I would do the following:
1) Use the log view option in the Server Manager to view all DHCP messages from /var/log/messages. DHCP is usually pretty verbose when it comes to problems, so you can try to see if it provides any insight.
2) Depending on what version of Windoze you are using, release all of the IP address leases. Sometimes, it refuses to let go of it's last IP address. On a Win9x machine, run winipcfg from the Run menu, and click on Release all. Shut down (don't reboot), and then see if it can get it's IP from the e-smith box.
I have had many issues support field travelers in my organization, and this is a very common problem.
Just my two cents tho, YMMV.