I've been using these two programs along with NetStumbler to learn about the networks adjacent to my apartment (about 5 reachable via pringles.) One of my neighbors runs a node SSID www.personaltelco.net, leaves his AP on, but not his gateway server. (Don't ask me why.) -PatrickSullivan
Multiple Tray Ping (Freeware) by Moxim Software
http://www.moxom-software.co.uk/
This program pings his gateway server periodically and shows the status of the last ping as a red or green light icon. It works very well.
IP Ultra Scan 2000 (Freeware) by Ultrajones Software
http://members.home.com/ultraj/
Is an IP ping scanner and port scanner. I haven't used the port scanning, for golden rule type reasons (and I wouldn't know what to do if I found them.)