Just guessing here:
You have serial 0 set to 172.16.1.1 255.255.0.0
You have Ether 0 set to 10.3.1.1 255.255.0.0
Go to to global config
type command:
router rip
then use command:
network 172.16.0.0
network 10.3.0.0
type exit, hit return
Make sure you have gateway of last resort set to the ISP router. Know though this gateway is on the router connected to the ISP, all other routers should point the gateway of last resort to the internal router connected to the ISP.
ip route 0.0.0.0 0.0.0.0 24.26.28.1
(not the 24.26.28.1 is not the right address, just an example)
If I made this a confusing mess, just say, "Hey fool. What in the heck are you talking about?"