Linux as an ISDN Based Remote Access Server?

Richard Becke asks: " I am planning to set up a Linux box as an ISDN-based dialin server for my company network. I have not been able to find any information about using multiple ISDN cards with Linux. We need to serve at least 6 simultaneous connections. Any ideas or tips would be most welcome. The question can be rephrased like this: How do i set up a Linux-based ISP solution?"