Problem solved. You guys now have full permission to laugh your behinds off at me.

Here's the deal. The problematic AP is at a neighbor's house, connected to me by CAT5. I was able to ping his machine because his son had disconnected the AP completely and plugged the cable directly into his machine. LOL. I didn't know this until I actually went over last night . . .

The access control settings on my router block all ports except the most necessary to keep people from hogging bandwidth with torrents and other P2P stuff. I accidentally blocked HTTP for 'guest' users though, and his MAC address was included in that list. When he plugged the cable into his laptop he was able to acquire a new MAC address and could then access the Internet, so when I called and asked if my friend could access the Internet, he naturally said yes.

Nothing to laugh about it, good you solved.
the only thing it's that a great percentage of post are like your #1 you never posted the scenario about AP connected via LAN cable at your neighbor's house, without that info. you start to receive answers based on what you posted, or receive no answer.