Tyrone,
It depends is the easy answer..
Do you want to be able to server external DNS? (to the internet) or just to 2 internal Subnets?
If the answer is two internal Subnets.. you could just try adding another IP address to your singe NIC..
Lets say that you allready have the subnet 192.168.0.* on eth0
and you want to add 192.168.1.* also.. all you do is:
ifconfig eth0:0 192.168.1.254 up
check ifconfig and you should have an eth0 and an eth0:0
eth0 will have whatever IP it had before and eth0:0 will have 192.168.1.254 or whatever you specify.
Hope that helps..
Andy