How do I connect my computer to a router for home networking without

[JOHN B]

sharing the internet? Here is my setup:
1 Desktop Connected to local Comcast Broadband Cable
(has 2 NIC cards installed)
1 Lynksys wireless router connected to Qwest DSL
3 Laptops with wireless adapters

Here is my Problem:
I want to share all computers on a home network for filesharing only. The Desktop needs a dedicated Broadband connection. and the Wireless Router will share the DSL for the laptops..

I have the Desktop Connected to the Broadband modem on one NIC and to the Router on the other NIC. How do I disable the DSL to the Desktop, from the Router, while keeping the LAN filesharing capabilities on? Alternately, How do i prevent the Desktops Broadband from being shared to the Router?

I know this sounds complicated, but if you understand this, then I assume you know as much if not more about this situation than I do and would love to hear some good answers. Thank you in advance.