sound in mono, how can i put on the 2 speakers ????

hello
i've got a divx in mono (sound just on one speaker)
how can i do to have the sound easily on the 2 speakers ???
3 months ago i used a little program (plugin i think) wich equalize the sound, and, more important thing, send the sound of one line on the 2 speakers
i can't remember the name

helppppppppppppppp

thanks

filou