DNS

Sir,

i am facing very strange problem. I have very small setup in my branch office. One ADS and in that ISA. it has some problem so i went there and i can’t recover that problems, i formated the ADS server , install and configure DNS till now every thing fine. But in this i have two NIC s one for local and one for external IP. so i installed in that ISA server. when i install ISA server the external IP is automatically regester in my LOCAL DNS. so when i check the NSLOOKUP i am getting error and if i ping with my local DNS it is pointing out external IP. i had done this type of sam e setup number of times with out problems.pls help me.