Adding wireless to a network

I am running a Windows 2000 Pro peer to peer network through a wired router. There are three computers on the network presently. I want to add a fourth computer but it is approximately 500 feet away across the street. I know I will need to change my router to a wireless router and add a wireless LAN card to the fourth computer. I have read that some of the new hardware can do this. I am willing to add whatever I need to accomplish this. What I can’t do is run cable. Please address the hardware issue with suggestions of products and models.