Connecting 2 networks to 1 server

I have a customer with a Win 2003 server, with 3 nics. One nic is to a secure hotel chain backbone network using a verizon 250k connection. The other 2 nics are disabled. We also have a business highspeed cable connection. Customer complains about the slow speeds and would like me to enable use of our highspeed connection while still remaining connected to the hotel’s backbone. How do I set this up?