Well FRAPS is your best bet... it is a piece of software specifically designed to capture on screen video and audio.
So if you plug your mic in and have your sound card set up to have the sound of your mic come out alongside the sound coming from your game (any soundcard can do this by simply enabling the Mic in the volume properties controls so that when you speak it will come out above the other sound) then just record your game using FRAPS and make sure audio recording is enabled and it will pick up everything for you.
-Cub. =o)
So if you plug your mic in and have your sound card set up to have the sound of your mic come out alongside the sound coming from your game (any soundcard can do this by simply enabling the Mic in the volume properties controls so that when you speak it will come out above the other sound) then just record your game using FRAPS and make sure audio recording is enabled and it will pick up everything for you.
-Cub. =o)