Adding second subnet to Win2k3 AD domain site

Good afternoon – I’ve read some posts on the subject but need some hand holding…

I need to add a secondary subnet to one of our AD sites. Existing site subnet is 192.168.1.x/255.255.255.0. I have a secondary NIC ready for use, and have created the new 192.168.3.x subnet in AD. I need communication between the subnets and looking for some explicit HowTos. Any assistance is greatly appeciated.