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.
Things like ZoneAlarm, Norton, McAfee and others just slow down your computer and give no better protection than Microsoft Security Essentials and Microsoft firewall. (That is not just my opinion) See this quote from Fred Langa of Windows Secrets...
Earlier this year, when Microsoft Security Essentials (MSE) was still new, I decided to put it to an extensive real-life test by making it the only full-time security solution on my daily-use and portable PCs. I then reported my initial results in the May 6 Link Removed due to 404 Error, "The 120-day Microsoft security suite test drive." I also promised future updates.
So here it is: after six months of full-time use on nine different systems, MSE looks like a solid winner.
For my tests, I used Windows' built-in firewall (on XP, Vista, and Win7) and a copy of Microsoft Security Essentials, which I allowed to run with its default settings. Over the past six months, my main PCs have been online 24/7 and my two portables have logged over 20,000 miles (32,000 kilometers) of use in hotels, coffee shops, cars, planes, ships, and other assorted public venues.
All the machines have remained clean. They've suffered no malware or virus infections whatsoever.
Good Luck