Taken from another forum I found when I just googled "mpga":
How can i convert Mpga to mp3 or wav ?
If I'm not mistaken, MPGA stands for Motion Pictures Group Audio... which in simple terms can be considered the long way of saying it's an MP3 file.
So, you shouldn't need to convert and mpga to an MP3 file. If mpga bothers you; you should be able to rename it to a .mp3 file and it should play fine in any MP3 player.
To convert the .mpga file to .wav, simply follow our online mp3 to wav tutorial at
http://www.zittware.com/Products/CDMaster32/mp3towav.html
If you decide not to rename the .mpga file as a .mp3 file, you can still select the .mpga file in CDMaster32's MP3 to WAV decoder. You can select the file by setting the Files of Type box in the selection screen to "All Files (*.*)".
THE GOOGLE IS YOUR FRIEND