XingTones was reviewed very favorably at
http://blogs.pcworld.com/staffblog/archives/000783.html, and they seem to think $20 is a bargain.)
And I found this
excellent explanation of the whole topic, including information on using Blazer (the default Treo 650 web browser!) to install ringtones, and a lot of information that also applies to the Treo 600, which is limited to midi files for ringtones.
From that article, you can see that for the Treo 650, any .wav file can be converted to a ringtone as follows:
1) Create the .wav file and extract the part you want to be included using software like
mp3 splitter (free).
2) Save the .wav file to your SD card.
Actually you can put it anywhere that Blazer can get to it, so if you like, you could even put it on a server.
3) Transfer the file to the Treo using Blazer.
Type "file:///<yourDirectoryPath>/filename.wav". You will be glad on this step if you kept it near the root of the SD card! Blazer should prompt you to save the file either into the Sounds application or onto the SD card. Pick the sounds application of course.
Caveat: Apparently PocketTunes will override the action taken on .wav files, so you may need to uninstall PocketTunes or find an alternative program for the transfer (like VersaMail, or RescoExplorer, or Initiate.)
4) Select the sound from Prefs for your new ringtone.
If I get the chance, I'll probably give it a try with RescoExplorer (which is already installed on my Treo), and see what happens. Let us know if you try this.