Custom ringtones are something that has been somewhat of a mystery while I hadn't researched how to do it, I figured it couldn't be that hard.

The process is simple...
1) Acquire an mp3 file of the ringtone audio
2) Convert it into a small .wav file. Probably fairly low quality is good to keep the file size small

If you have bluetooth on your computer, then
3) Send it to your Treo using Bluetooth. It will automatically go into your Treo sounds collection.
If you don't have bluetooth, then there are instructions to
3') use Versamail after you copy the file to your sd card.
And if you don't have Bluetooth on your PC or use Versamail on your Treo?
3'') Well, I'm not sure yet. I guess there's a bit more research to be done.

To enable the ringtone, you simply finish up this way:
4) Select the file in Prefs...Sound & Alerts...Tones