It won't work with your DM because jad files are OTA if I'm not mistaken. You'll have to install it that way. Somebody may know a way around that, though. I think I read a post recently about transferring the file to your media card, and then to desktop manager or something. I can't remember. You should search the forums and I'll bet you'll find the answer. This site is full of information!
if you're trying to install it from your memory card, you have to have all the .cod files that go along with the .jad file or else you won't be able to install it. if you notice, the .jad file is usually around 1kb in size or less.
otherwise you'll have to install it OTA from a site. the jad file alone is useless.