DNS help needed - tricky one this!

We're having trouble with too many DNS requests overloading our Win 2k NAT (Network Address Translation) server and causing it to crash. Up until about 2 weeks ago everything was working fine.

We've used some port monitoring software on our NAT server which shows the traffic coming to it via our Windows 2k domain controller. We've also monitored our Win 2k domain controller which shows the traffic coming to it via our Win XP workstations.

It's coming from the workstations, to our Win 2k domain controller/dns server and then over to our Win 2k NAT server. The domain controller passes it to the NAT server via the default gateway - it does this passes it because it can't resolve the name itself (an internet name (www)) - the NAT server has our ISP's external DNS addresses.

We've tried eliminating the NAT server by using an ADSL/Broadband router instead but still the traffic continues. It's bringing our net connection to a complete standstill.

Any help would be massively appreciated. We live in hope!!

Cheers in advance for this one.