In a college's internet laboratory:

1. Network has 2 different ISP net-connections.
2. I want the both net-connections to be available to all clients.
3. My Linux-server has 3 LAN cards:
eth0 : connected to ISP1
eth1 : connected to ISP2
eth2 : I want to to circulate internet received in eth0 & eth1 to my intranet.
HOW CAN I DO?
4. I do not know how to combine 2 ISP connections into one.