Moggs are a version of .ogg (ogg vorbis)....most commonly found within the Rockband game for Xbox etc. They are a little like a zip file too, because they can contain more than one sound file. The only way i know of extracting to a useable format is as follows:
1. ....get Audacity, the free audio editor, go for version 1.3 (Beta)....some people experience problems with the older 1.2 version...me included.
2....once you have downloaded and installed Audacity, go to "file"...and "open"....select any .mogg file you have been lucky enough to find!
Audacity will then read the .mogg and open it like this! Image
What you see is the song you dowloaded as a multitrack...drums, bass, guitar, vocal etc. You can then do anything you please with it!...or nothing at all...just save it as a more convenient format.
To save to a useable format, go to "file"..."export multiple"...select the format of your choice...Wav, Flac, mp3 etc....and you are good to go!