Termination of 2 internet connectivity from 2 different ISPs.

Hi,

I have internet connectivity from 2 different ISP, one thorugh Vsat and other fron SCPC link, i want to use internet connectivity through SCPC link as primary and Vsat connectivity as back up. please explain me how can i achive this? Vsat modem out put is ethernet while SCPC modem put put is serial.
i want to achive this through Cisco router or Cisco firewal.
Please let me know ASAP.

Thanks in advance
Bhoopendra P Singh