But you'd have an easier time getting Windows Media Player to cook you breakfast than you would getting it to convert WAV to MP3; it's not by itself a file converter. For that, your best bet is a third party audio converter. I've been happy with dBpoweramp's free MP3 converter, but there are plenty of good freebies out there if you look around. bN1p.

how to convert mp3 to wav on windows