I tried installing MTJ 1.1.2 from http://www.eclipse.org/mtj/, but after the restart, no new options appeared that would indicate that the plugin is even there. As the latest release is for Helios, I am afraid that the plugin no longer works with Juno and later.
Is it still possible to develop J2ME applications with Eclipse? If so, how? If not, what are the alternatives?
You don't need a plugin at all, you can point eclipse to the midp and cldc jar files, and write your own ant/antenna script to package a midlet.