Currently I have two ways of Connecting to internet ie., I am using two broadband connections they are Hathaway broadband and airtel broadband through two ethernet cards one is built into motherboard and another external,they all connect to my access switch S5700-28C-EI.

I am able to browse internet using any of the above connections. The issue is Hathaway broadband is frequently disconnecting and airtel broadband is providing services without interruption.
Hathaway is providing data download at very low cost and airtel is providing data download at very high cost.

I am using openSUSE12.3 as my operating system. When I issued the command ifconfig it is showing message as Hathaway is assigned to eth0 and airtel is assigned to eth1.

I want to achieve the following goals
1)when I download any file the system must use Hathaway ie., eth0
2)when the Hathaway broadband disconnects the system must immediately switch to airtel broadband ie., eth1

This would usually be accomplished using the "metric" attribute of each route - which tells the kernel the cost, performance, etc of each route. Based on this information it can then route traffic properly.

Unfortunately from what I can tell, NetworkManager doesn't let you set this for automatically determined routes - only for manually specified routes.