If you are upgrading your computer from Mac OS X 10.4 (Tiger) to 10.5 (Leopard), the upgrade should be seamless.
If you are doing a clean install of Leopard (i.e. wiping the hard drive first) or you want to back-up your PandoraJam prefs before upgrading, you should back up the following folders and files:
Once Leopard has been installed, simply copy the files to their original location. Security information such as your Pandora and Last.fm login details will have to be entered again.
As always, if you have any questions, e-mail firstname.lastname@example.org.