See the installation instructions for the specific requirements for Antelope. Antelope does require Java 1.4 or later as it makes use of both java.util.logging and java.util.prefs APIs which were introduced in that version.
Due to changes in the jEdit API, Antelope plugin versions prior to 2.60 are for jEdit 4.1, versions 2.60 and later require jEdit 4.2 or later.
Antelope does require Ant 1.5.x or later, which is a separate download. Ant is available from http://ant.apache.org. Antelope has been tested extensively with Ant 1.5.x, and seems to work with no problems with Ant 1.6.x. If your development environment already runs Ant, you have everything you need to run Antelope.
A note about Ant 1.6: With the release of Ant 1.6, the Ant developers have choosen to package the classes that formerly were part of "optional.jar" into a variety of smaller jar files.