This one can record, tho it will record everything that can be heared, (also the music, when you playsound in the same time) as far as I see.
http://www.blitzbasic.com/codearcs/codearcs.php?code=845
But there is also some code that lets you control the mixer settings, so maybe you'll be able to set the recording settings to "record only from microphone" while leaving the player settings unchanched. well, I didn't try it:
http://www.blitzbasic.com/codearcs/codearcs.php?code=847
http://www.blitzbasic.com/codearcs/codearcs.php?code=845
But there is also some code that lets you control the mixer settings, so maybe you'll be able to set the recording settings to "record only from microphone" while leaving the player settings unchanched. well, I didn't try it:
http://www.blitzbasic.com/codearcs/codearcs.php?code=847