on the server, go to the add remove programs and add the network monitor (should be there somewhere)

this is a relatively simple packet tracking utility, with the DHCP server installed, you'll have a few presets, so you can see if the server is getting the DHCP dicsover packets, and if so, if there is a responses..

If the server sees no broadcasts from the clients, then it's a 2k issues, install a packet tracker on one of those systems and track the info.