ENDIAN Firewall - How to use Multiple ISP links at the same time

Hi , Here is my scenario,

In our orgn. we are having 15 PCs. With fedora 14, ubuntu 10.04, centOS 5.5, Mandriva 2010.1 and redhat 5.5. Not even a single windows system. We are getting Internet Connection from two ISPs named BSNL and Sify. Both are 1 MBps. We have connected the BSNL line to a wifi router so that all the machines can access Internet through Wireless LAN card in the system. now what we are doing is, if BSNL is down then we are again plugging in the sify cable to a router and we are re-configuring the router again to work with sify and vice versa. we need a solution to give both the ISP lines in a single machine and to get an output from it as a single line. by having three LAN cards in that. So that if one ISP is down then the other one takes up automatically. Please help me how to configure the Endian Community Software. by installing it in a machine.