There are two pieces of software that you need to load on to your computer. First is the BlackBerry Desktop Manager, and the second is the BlackBerry device software that matches the version found on your BlackBerry. Once that second piece is installed, you should be able to load applications to the BlackBerry using the Desktop Manager.
If you installed another OS to the BB is that OS still installed on the pc you're using? If not, you can simply install to the pc the same one you have installed on the BB. Then it won't upgrade. You only said you were using an 8320 on TMobile. You sound like you've never installed an OS before yet you've got a different OS installed and other languages.