ACM files belong to a game called Fallout. From what I read, it seems that these files are a kind of .mp3 files using LAME ACM Codec. To export files in mp3 format that you want, you must use Adobe Audition. Some time ago you could use Cool Edit Pro but was integrated into Adobe Audition.
To convert your files, load the mp3 you want into Adobe Audition, and choose EXPORT from the main menu. You will have the possibility to chose from a wide number of settings when you are performing this action.