text: Yes you can.  Download Netstumbler and Ethereal (both free) and give those a try.  Ethereal is a freeware Sniffer, and depending on your wireless network card's internal chipset, you may or may not be able to sniff the lower level wireless frames, which would have MAC addresses, SSIDs, and everything else too.  But try NetStumbler first, it works great, and it will detect all other wireless LANs in your proximity and tell you what channel they're on (so you can detect if a neighbor is interfering with you) and if they have security turned on, etc.  Say for example you see your neighbor on channel 6 (common default) and their signal strength is good, then you can change your AP to channels 1 or 11 to minimize interference.