Finally, I've found it! (This has been around for a while, but whatever. I just found it now.)
How to internally record audio on a PC:
1. Make sure you have Audacity on your computer.
2. Go to Recording Controls (Control Panel --> Sounds and Audio Devices --> Audio --> Sound Recording --> Volume...)
3. Click Options --> Properties, and make sure that Stereo Mix is checked in the list of available recording inputs, and that Volume is adjusted for "Recording."
4. Click "OK," and under the Stereo Mix slider, click "Select" and raise the Stereo Mix volume all the way up.
That's it! You can now record internally.
For more help, click here.