HELP!!! trying to set up home network

I have 2 laptops and a desktop. both laptops have wifi enabled and have vista. my desktop (XP pro) has no wifi and is connect to the internet by the modem. my modem is wireless and i also have a wireless router that i am not using. this is my current set up. all my computers are in the workgroup "WORKGROUP" and i can transfer files between the fine. I want to move my desktop to a different floor of my house and i can't bring my modem with it. i was wondering if i could still get that computer connected to the internet somehow? maybe by using my wireless modem or something? any help is appreciated.