You can download the plugin at: ftp://jext.sourceforge.net/pub/jext/plugins/AntWork.zip
You have to enable the Jext Console to see the Apache Ant output (menu: Edit->Options... - General Panel), because the Ant messages are redirected to the Jext console.
You can configure the Ant call in the Jext menu: Edit->Options... - Plugin Options - Antwork Plugin Panel; here you can set the ant home directory and the path to your build file.
You can start AntWork in the menu: Plugins->Ant->Work Now! In the appearing dialog box you can enter the target which you want to compile.
If a javac error occurs in the ant run an error-list opens within Jext. With a double-click on the error-message you jump to the error in the specified java text file.