Nero 5.x has an option to remove the vocals from songs as they are being written to CD (Karaoke plugin, I believe). I've never tried it, but it works by removing content common to both channels, so its effectiveness will vary depending on how the original recording was done. Not sure if Nero can modify WAV's directly, or if you must first write it to CD and then extract the song back off the CD.
Best regards,
Floyd