I don't know a lot about your phone, but let me tell you everything I know...
1. How to send a ringtone from a phone to another
For old phones (like Nokia 3330), you can send them from the Composer. They will be considered as messages. For new phones, Nokia decided not to let us send ringtones to other phones for some reasons, but if you have a program called "SeleQ," you can send any file from your phone to another one via Infrared, Bluetooth, or Multimedia.
2. How to send a ringtone from a phone to a PC
The only way to do that is to send them using SeleQ via an Infrared device or Bluetooth (which you should install in your PC).
3. How to send a ringtone from a PC to a phone
You can send any kind of ringtones using the Infrared device or Bluetooth. Otherwise, you can upload the tones to the Internet, then using the phone's WAP browser, enter the location of the file (for example "http://example.com/something.mid"). I also heard that some sites can send them somehow to phones without any cables or stuff.