Child domain in win 2003 network

I have an existing forest admin.local(192.168.1.20) and i want to add a child domain child.admin.local( 2 NICs – 192.168.1.25 and 192.168.7.1) and i will have other work stations connect to the child domain’s 192.168.7.1 leg. the gateway (to the internet) is 192.168.1.10. all the work stations connected to the child domain need to be able to get to the internet. I dont have a router. Please, how do i configure the child domain. thanks.