DNS in WINDOWS 2000

Hi,
I have just installed windows 2000 with Active directory and setup DNS as the server which is say 172.16.8.1. I have also installed DHCP & WINS on the same server.
I have a firewall and leased line access to the internet.My ISP have given me 2 DNS IP numbers for the internet access which i added in the TCP/IP settings.
I can either access the internet or the internal local network at the same time but not both.

What am i doing wrong.

Could you pls help.

Charles.

The problem is this.
If i set the external DNS info as the preferred DNS,then i can connect to
the internet – no problem but internal connection is very slow.
Eg: Outlook takes extra time to connect.

If i change the DNS to local DNS then i can’t connect to the internet but
outlook starts up quickly.

How can i resolve this ?