WRT54GL configured as ethernet bridge is the best option IMO. Only costs $50 and works flawlessly with Tomato or DDWRT firmware, and you can connect 5 computers to it. And you can always reconfigure it to be a router or wireless access point later. Wifi cards can't be reconfigured to be anything else, and they only serve one PC at a time. They're not a smart buy when you can get a good multifunction device for the same money.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833124190
http://www.newegg.com/Product/Product.aspx?Item=N82E16833124190




