You haven't used the Launcher to log on, therefore you are "plazeless". You cannot search for people or Plazes by radius.
Apart from binaries there is also a Python launcher . That is ok, if Python works on your system. So I was looking around for a signed Java Applet which gets access to the machines MAC address . I am not sure, if at all, a launcher is programmable as signed Java Applet , but it would be fun to have a platform independent Launcher anyway. Maybe there will even be a non-Java Plazes Launcher Firefox extension one day, but that is just a guess.
That's all a bit hard about the very hardware near network programming in Java because there's no abstraction for this now. But perhaps in the near feature I will give them a try (and write some notes in my blog).
There is actualy a Plazes.com launcher for Java now. This launcher is using native methods to check the plaze. The Plazes launcher itself is available as Java Webstart Application on: http://www.cyber-junk.de/ws/plazes/jwsplazes.jnlp