JAR files contain program code and JAD files contain a desciption of that code. Consequently, JAD/JAR is one way to distribute apps.
However, your BB prefers COD files that contain program code and ALX files that contain descriptions of that code. Consequently, ALX/COD is the BB version of JAD/JAR.
You can convert between the two. There have been attempts to automate the conversion but they are not always succesful. Google JAD2ALX.
You can recompile JAR files to COD files using the IDE provided by RIM. You can write your own ALX files using notepad.
Tutorials can be found online.
Often, you can open a JAD file and copy the urls to COD files. Download the COD to your desktop and write a new ALX file that reuses values from the original JAD. Install to your BB using the DM.
This works for all themes and apps
Posted from my CrackBerry at wapforums.crackberry.com