Connect 2 Cable Modems into 1connection

I've 2 cable modems, each with different ISP. I plan to connect that 2 cable modems into 1 connection and share it to other computers as load n balancing connection. I have read about nexland router but the router seems very expensive for me $399

Is that possible to connect this 2 cable modems and share it to other computer using a server software ?? if does that means i have to install 3 NICS on my server (2 for my cables, 1 to share out other comps) but what kind of software ??

Anyway i want to use w2k advance server for sharing this connection.

Thx in advance.