IIRC I used different tools:
1. RAD Video Tools to convert the video file and extract the audio (since the final audio quality was horrible)
2. BeSweet to convert the WAV file to mp3
3. VirtualDub (probably VirtualDubMod) to mux the video and the audio streams
I know that it's not the simplest way to do it, but I tried several tools and the final result was never the one I wanted (bad video, or bad audio, or desynchronized streams, or the inability to choose the conversion parameters)
Probably there are better AllInOne tools, but in my rapid search I wasn't able to find a valid one.
Probably on doom9 forum you'll find other valuable tools
