xp taking up two license on NT server

I have xp pro on five machines on the network. The work great but on my NT server event log…I keep getting the out of license error message. When I go to the license view, I see that all my xp machines are using two licenses. One with the computer/NT logon username and the other with workgroup/ NT logon username. Our NT domain is called workgroup (which I inheriated from the previous network admin – I will change it by the end of the year when I get the go ahead for upgrading to Win2k server). In the mean time, how can I fix this issue. Please help?