Many thanks for all your help.
All the workstations are in 192.168.1.0/24
Most of the the workstations only have one connection "Local Area Connection". There are one or two guys in accounts with modems for banking s/w.
Around 20 of the workstations already have two DNS servers set(required for an app they use). The rest do not have a DNS.(I've noticed netsh removes any existing DNS settings, but I guess I could use forwarding to get around that).
The new DNS server(DNS intergrated into AD, with Dynamic updates) will be 192.168.1.40/24. Other than that thats it.
Regards
p.s By the way. The reason for doing this will allow me to migrate the workstations from the NT4 domain to the 2003 domain(which will have a DNS server 192.168.1.40). To do this I'm using the Active Directory Migration Tool. Currently I do not have a DNS server in my office, those 20 workstations mentioned above are pointing to a DNS server on the internet.