DNS PROBLEM IN WINDOWS 2000

Hi all I am having linux server as my primary gateway which is configured as DNS server.
I am facing a problem which i am not able to solve
all my windows clients are connected to linux server for internet and windows 2000 for database
machines running windows 2000 is havnig internet connectivity problem. If net is down and if we change the dns server in preferred dns servers the net is coming after some time net goes down and again ive to follow the same procedure.
can any body give me a goot solution how to solve this problem