[SIZE="5"]For Windows 7/Vista you can go to Start>Control Panel>Hardware and Sound>Under Sound Tab}Manage Audio Devices>Recording>And make sure it's your Sound Card/Driver being used (Stereo Mix, Sound Out, etc.)[/SIZE]
On your desktop, click Start and go to control panel and click the "Sounds and Audio Devices" icon. Click the "Audio" tab on the Sounds and Audio Devices.
After that, click "Volume" on the 'Sound recording' tab. A new menu should pop up.
[Image: http://i94.photobucket.com/albums/l115/gaara12_01/untitled-5.jpg]
Now at first for me at least, only these tabs showed on the menu and "Microphone" was checked. This is the cause for low/no sound recorded for me.(the recorder will only be able to record in-game sound if your sound source is checked instead. My sound sources come from Stereo/Mono Mix so one of those two have to be checked, many computers have different sound sources (i.e. Wave-Out Mix is the sound source instead of Stereo Mix)
[Image: http://i94.photobucket.com/albums/l115/gaara12_01/untitled-6.jpg]
*If you do not see your sound source at first, click 'Options' then 'Properties'. You should see something like in the picture (but your sound source unchecked). So now check your sound source.
Note: If you do not know which one is your sound source, usually your sound source would be one of the first ones on the list. To find out, just check the one you believe it is and record in-game and check to see if there is sound recorded (use a skill for sound).
[Image: http://i94.photobucket.com/albums/l115/gaara12_01/untitled-7.jpg]
Once you done that, the Recording Control should include your sound source now. Now check "Select" for your sound source. Also make the volume for the one selected close to mute as shown, otherwise the sound recorded in-game will be too loud (It was too loud for me at least, but you should test to see what sound level is the best for you. It's not always very low or Max Volume.)
[Image: http://i94.photobucket.com/albums/l115/gaara12_01/untitled-8.jpg]
So now you should be able to record in-game sound via the built-in recorder. If you have any questions or need any clarifications, post it.