Mpg321 is an attempt to write a free replacement to mpg123, because mpg123 wasn't under the GPL. Unfortunately, it lacks some features, most notably, the keyboard control. There is also madplay which can also play MP3 files, and does have keyboard control. It is installed with the Mad library, which is probably already installed since it's required by mpg321. The old mpg123 is in the Extra directory of the Slackware 9.0 FTP site. It was completely removed from 8.1, but I think, was put back by popular demand. I'd say either look at madplay, or put the old mpg123 back.
