Try Format Factory. Not sure what format yours are. But FF is excellent quality.

dulcie, hello. I'm expect that there may be some free solutions for recording MIDI files to WAV, but the only solution that I know of is QuickTime Pro. The quality of a MIDI file is greatly influenced by the quality of the sound samples that are used to play it back. Sometimes these are referred to as "wavetables" in the PC arena. I've always felt that QuickTime has a rather good wavetable set for one that is free. To my ears, MIDI playback in QT is much better than in WMP. The *really* good sounding wavetables are commercial products.

If you have a way to record the sound playback from your PC's audio card, you could use the free version of QuickTime for playback and record the output to a WAV file.