Just to clarify: You have 2 NICs on your computer, and you have the cable modem connected to one, and the wireless router connected to the other.
I would make it easy on yourself and connect the wireless router to the cable modem and get wireless NICS for both computers and have them connect to the wireless router.
Another solution is to just get a wireless NIC for the other computer and have it connect to the wireless router. You would have to set up ICS (Internet Connection Sharing) on the computer in your room. Use the built-in Help and Support function in Windows XP to find out how to use ICS.
If you have any questions about ICS or otherwise, post back.