Active Directory Login

I have a 2003 Win serve which is the AD to the network. Recently we carved the network up into 5 subnets due to growth. However machines that are not in the same subnet as the AD now have problems connecting to Networks shares and authenticating against the AD.
What needs to be changed in the AD t make this work? I have created fixed routes on the machine to ensure that traffic from the other subnets is routed correctly. I am using a Cisco 3075 to manage and create the subnets.
Any help is most welcome – thanks