On the movies tab, set to 'Detect best sound input'
Click start/control panel/sounds and audio devices/advanced, to get the menu pictured below (assuming you have sound blaster card)
Under microphone untick 'mute'
If you can now hear your own voice when you talk then this procedure will work for you.
Your voice is now feading back through your speakers/headset and can be recorded by Fraps.
Normally Fraps records ingame sounds & other players talking but not your voice, however by hearing your voice as well, this enables Fraps to record it as well.
The volume of feedback is a key factor to tinker with latter to make sure your voice is load enough in-game and on video playback.
Under microphone click advanced. Make sure '+20Db boost' is ticked.
This is the same setting as 'Boost mic gain' in BF2 Options/audio menu
Inside BF2 options/audio menu, lower game volume effects to 20-40%.
This is a key factor to play with latter because in-game sounds are loader in the video then when ou hear them live in game.
If the setting was 100%, the video in-game sounds would be loader and drown out the voices recording.
-Note- this is made for BF2 but will hopefully solve your problem.
-Source-

Click start/control panel/sounds and audio devices/advanced, to get the menu pictured below (assuming you have sound blaster card)
Under microphone untick 'mute'
If you can now hear your own voice when you talk then this procedure will work for you.
Your voice is now feading back through your speakers/headset and can be recorded by Fraps.
Normally Fraps records ingame sounds & other players talking but not your voice, however by hearing your voice as well, this enables Fraps to record it as well.
The volume of feedback is a key factor to tinker with latter to make sure your voice is load enough in-game and on video playback.

Under microphone click advanced. Make sure '+20Db boost' is ticked.
This is the same setting as 'Boost mic gain' in BF2 Options/audio menu

Inside BF2 options/audio menu, lower game volume effects to 20-40%.
This is a key factor to play with latter because in-game sounds are loader in the video then when ou hear them live in game.
If the setting was 100%, the video in-game sounds would be loader and drown out the voices recording.
-Note- this is made for BF2 but will hopefully solve your problem.
-Source-