Simple editors (that let you see and hear the wave-form, and then copy, cut, and paste it) are available for WAV/AIFF and MP3 files, but for AAC/MP4 I haven't found anything useful. *
    Are any simple/cheap wave-form editors available for MP4? {and are some for Macintosh, or only Windows? for MP3, many wave-form editors are available for Windows, but for Mac the only one I know about is Audion}

    {* QuickTime6-Pro can do simple editing but -- since the window is very small, and there is no way to "zoom in" on a short segment of a long file -- it's useless for splitting a large multiple-song file (made from an audio tape) into separate songs, or to "trim" space from the beginning or end of a song, because (for a long file) the smallest time interval you can select is several seconds, not (as in WAV or MP3 editors) milliseconds.}

Mike

New web version of NERO (will be available in a day or two) will have AAC (trial) support, and you will be able to open and edit file inside NERO wave editor.

A day or two!? Sounds great... Sooner than I expected...