WinXP Workstation DNS problem

Lately, I found a couple of my clients WinXP workstations are displaying this DNS resolution problem: It will resolve any domain host NETBIOS name to 127.0.0.1. I checked on the DNS, DHCP & RRAS servers on the domain controller and did not find any problem with them. Apparantly, the WS are hit by something lately. Did anybody have similar experience? Because of this problem, those WSs cannot access network resources on the server anymore. I appreciate any help in advance.