If both machines are on the same Workgroup, have file sharing turned on, are password protected, have one or more items shared (folders, files or drives) and are only using the Microsoft firewall and anti virus, then you should be able to see all computers on your net. On my network I have four computers. Two are Windows 7, two are Windows XP SP3 and all but one desktop computer are wireless. Being wireless should do nothing to help or hinder your being able to see them on your map.
Go to Control Panel-All Control Panel Items-Network Map. If you don't see your computers there, is there a sentence at the bottom of the page that says "Click here to see all other devices"? Click on that and you should see everything on your network...
