Audio Fix Help Wanted

I came across some music performances that I recorded onto my hard drive about two years ago which I burned to CD. When I recorded them, my video card (ATI All In Wonder Radeon 7500) wasn't completely set up right which resulted in having only the right audio channel recorded. These performances are Mono so I didn't miss anything but what I'd like to do is re-copy them to my hard drive & put the right audio channel into the left as well. Does anyone know of a "freeware" program that will do this? Thank You.---Bill