If the "background music" is in the recording, about the only thing that you can do is take the Audio file into a program like Audition, or Soundbooth. Look at boosting the voices (start working around 250Hz, but experiment upwards too), and then EQ'ing down the other frequencies. You can possibly gate some of these, to bring the voices more forward. Remember, all sections of the music in those frequency ranges will also be boosted.
It's best to record the dialog without any background, except maybe room ambience, and then add any music in post production.
As 'The Wine Snob' indicates, you can pull some really good background sound reduction technics using Soundbooth. If you wanted something really rough that might work in Pro:-
Switch you audio file so you can view them as waveforms and increase the scale to the highest point possible, then cruise through the file with the razor tool and cut the file at every point just before and after the spoken lines. This way you could raise the audio gain on the spoken line slices and lower the audio gain in the clip slices that are just the background music. This might be enough for the result you need.
Now, this is for Audition, but might work in SB and maybe even programs like Audacity.
Some have had luck by making a copy of the Audio Clip, using Remove Vocal Effect on the copy, then choosing Invert and doing a downmix the two. Might be worth a shot.