Ok, I will assume that the router is Linksys (Wireless). Now when you say wireless card, are you meaning that it is a card for a notebook computer or a desktop.. What you do have to know is the model number, it is written right on the card. Go to Linksys.com and download the driver for that specific card to a CDR, note it will be too large for a floppy. (unless of course you have the drivers that came with the card) Install the software first and follow all three steps. Go with the defaults, that is yours best bet. Then install the card. NOTE: Install the software before installing the card. You should be connected in no time. I will have to assume that the primary computer with Win XP and the MAC are connecting with no problems. You still didn't make it clear what OS is on each computer....don't worry about the MAC, we know what OS it uses. Is the primary computer XP? Is the computer that you are trying to network XP? Is the computer that you are trying to network notebook or desktop?