XP machines + Default Gateway has same IP for IP Address and Gateway

I have a Windows 2000 Server environment and Windows XP workstations….The workstation are randomly pulling their own IP addresses as the Default gateway….DHCP scope has default gateway set correctly…..has anyone seen this before?? also sometimes they have both IP’s….the router as the default gateway and the local IP address as a default gateway? These are local pc’s not VPN pc’s.