I was trying for a wile to get some themes in to my BB8320 when I finally got it. Here it is as follows:
1. Find the .JAD file you want to install on your BB
2. Google Blackberry OTA LOADER and Download it!
3. Unzip and run OTALOADER.exe
4. Copy the link of the .JAD file you want to install and paste it into the address bar in OTALOADER
5. The .JAD file will be converted into several .COD files and one .JAD file
6. Browse your SD card using your computer and create a folder named "theme"
7. You will then copy all the files created by OTALOADER including the new .JAD file to the "theme" folder.
8. Disconnect your BB and open the MEDIA ICON, Hit the Berry button a menu should pop up. Select explore.
9. Find the "theme" folder and then open it, you will see the files you just copied.
10. Find the .JAD file and open it. You will get a menu, click download.
11. you will then see a progress bar installing the files, soon followed by application successfully installed.
12. Now Exit. go to >options>theme> and look for the theme name you just installed. and select the them. theme should be applied after a few moments.
I have only tested this with themes , but i believe it should be the same with other applications.