Hi Krishna,
Which traffic you wnat to load balance.
If you want internet traffic to be loadbalance then configure the default routes like below...
0.0.0.0 0.0.0.0 Serialinterface_IP
0.0.0.0 0.0.0.0 FastEthernet_interface_IP
Hope this helps you...
Please click on the correct answer if this answered your question.
Regards,
Naidu.