I know ringtones are just .mp3 files (at least mine are) and i just send it using bluetooth. Just remember you have to go to the media portion of your phone, hit menu, receive using bluetooth. That seems to work for me (i also have a microsd card so i don't know if it works without it, havent tried). For the most part i just found OTA themes and installed it that way..
If you want to save memory on your BB, get a media card. You can transfer ringtones and music onto your media card and then set them up! It's real easy and you won't run into memory problems.