Help with recording

[Your Computer]

The Audio API of Windows XP does not easily allow for recording from both Stereo Mix and from Microphone. For that reason you will not find many programs that allow you to pick two devices to record from. It wasn't until Windows Vista that they revised the Audio API to make it easier for developers to not only allow for recording from both Stereo Mix and Microphone but to also choose which program(s) to record from while ignoring every other program.

In other words, it is not your fault.

One possible alternative, though resource heavy, is to have two programs recording at the same time: one of them the game, the other your microphone.