win 2000 dns

I just set up a win 2000 server ( domain controller) and 15 win 2000 workstations.I have pointed all workstation to the DC as thier DNS server and set the server to forward to my ISP( have also check the box do not do recurvsive)after doing this, all the workstation are very slow to access the internet, also the server is slow to access the internet, if i add my ISP’s dns servers to all workstations and the DC as additional dns I can then access the internet fast. Is this setup ok, what my I bedoing wrong
The server is not the root server and I have not deleted the root hint file. I have a dsl connection with a linksys router, the router is the default gateway.