Two Network Card in a NT’s Workstation

I have the 1st NIC card configured with IP N?A and gateway N?AA : This allow me to access Internet.
I have the 2nd NIC card configured with IP N?B and gateway N?BB : This allow me to access another Network.
With this configuration I cannot access to Internet or the other network.
If I want to access internet I have to remove the N? gateway BB (and keep the N?AA)and restart the computer.
If I want to access other network I have to remove the N? gateway AA (and keep the N?BB)and restart the computer.
How can I avoid restarting the computer ?