I need a simple program for editing mp3 files on my Mac (10.3) It
needs to show a waveform so that I can visually see the in and out
points and an easy way to save the edited cut for burning to CD with
Toast. Nothing fancy, basic, easy to learn. Something like SoundEdit,
the old Classic standby. Shareware is good, at least a timed out demo
version for now

I would recomment pro tools, it is free and works on mac.  It is
actually the same program that many professionals use.  Your should
give it a shot

Take a look a the programs here:
http://www.apple.com/downloads/macosx/audio/

I went to their website and could not find an OSX version, indeed,
reading further, it doesn't even work in Classic Yuck !
I quote
"Classic Mode under OS X is also not supported. If you have a
dual-boot system with both Mac OS 9 and OS X, you must choose Mac OS 9
as your startup system either in your Startup Disk Control Panel or by
holding down the Option key during startup to use Pro Tools FREE.
Systems that can only boot in OS X cannot be used."

I think you will really like Audacity -- the multi-platform (Windows,
Linux, Mac OSX) audio editor.  It even has VST support for adding a
wealth of effects to your audio.

Its open-source and freely available.  You can download it for free here:

http://audacity.sourceforge.net/

I HIGHLY recommend it and it sounds perfect for what you want.  AND ITS FREE!

I also would HIGHLY reccomend Audacity. This will handle mp3s as well
as OGG-Vorbis, AIFF and WAVE files. Make sure you have the LAME mp3
encoder installed right, and you are set.

As for protools: It is NOT AT ALL free. Their demo version is just
that: a demo. The base professional software runs for $600 and the top
of the line system runs upwards of $15 grand minimium, EXCLUDING host
hardware.

As for the OS 9/X confusion, ProTools is true cutting edge technology.
It takes a while for them to port it. The free version of protools is
meant to be a learning platform for an LE or HD ProTools environment.
It runs under 9 and will soon run under X, but it is NOT for the
casual user. Protools is the 747 of audio.

Audacity is your Honda. I use it under OS 10.3.3 almost daily as a
companion to Digital Performer. Their website:
http://audacity.sourceforge.net/ also has some tutorials. They have
not only a waveform display, but also some other interesting display
modes to play with. The program includes some interesting plugins if
you want to cut noise or even do remixes. Happy listening!