For MP4, try "mp4box" --
http://www.aziendeassociate.it/cd//gpac/dev/MP4Box.7z
For AAC, you can play them with a recent version of WinAmp afaik, but in case you can't,
you can decode them to WAV with "faad" and possibly some tools from this site:
http://dspguru.doom9.net/