Do you have a memory card installed? If so, plug in the Bold, and when it the Bold asks if you want to turn on Mass Storage Mode, click "Yes", and the memory card will show up on the mac desktop, and you can drag and drop music/video files into the appropriate locations on the memory card to your heart's content (or until the memory card's full, whichever comes first
Hope that helps. Desktop Manager only runs on Windows, and PocketMac has given me nothing but problems. Fortunately, for what you want to do, neither is required.