There is really no "correct" RIM package. It depends on your Blackberry target. The most common JDE's currently would be 4.2.1 and 4.3. You'll need to download and install the JDE, a recent Sun JDK, and (optionally) additional simulators, based on your target system. All of this is found on
BlackBerry - BlackBerry Developer Program | Support, Downloads, Knowledge Base, Community
It is important to note that your compiled code will be forward, but not backward, compatible. In other words, if you are compiling for a 4.2 target system, don't use the 4.3 JDE.
The JDE creates the required COD files "out of the box". You may have to set up some environment variables (like PATH) to insure that the JDE finds your Java compiler. You choose the simulator using EDIT / PREFERENCES / SIMULATOR on the JDE menu.