I don't know if AntsP2P is still under development and if there are still active nodes. The last release was in January 2008.
A note about Java on the
AntsP2P-Website:
NOTE: We decided to move the ANts network to the newest (and stablest) java release jre1.5 so please UPGRADE!
The newest Release files are here:
http://sourceforge.net/project/showfiles.php?group_id=106782&package_id=136701Which Java virtual machine do you have installed? (What's the output of "java -version" on the console?)
A big problem with actual Java programms: They run well on Sun's JRE, but not really on open source variants like GCJ or Kaffe... I don't know if this is still a problem.
(Ubuntu Linux installs OpenJDK as default, with this JVM it's not possible to run actual software like I2P or other...

)
Greetings,
Nemo.