If you can't enable the "Wave-Out mix" ("Stereo Mix", "Record What you hear") on your computer (this happens with both internal and external sound cards), you can record sound with software that doesn't need the Wave-Out mix / Stereo Mix for recording audio from sound card:

• Freecorder 4 (freeware sound recording program),
• Replay Music (shareware sound recording program that can split and tag songs automatically),
• Replay AV (shareware stream recorder that is good for scheduling online audio recordings),
• Replay Video Capture (shareware screen recorder that allows to record both audio and video),
• Replay Media Catcher (shareware stream recorder that can record audio from your sound card as well),
• Ask & Record Toolbar (freeware sound recording program),
• WM Capture (shareware screen recorder that allows to record both audio and video),
• Virtual Audio Cable (shareware software that creates a virtual audio device)

Most programs work not only in Windows XP, but also in Windows Vista and Windows 7. In fact these programs can be the only way to record audio from your sound card on computers with disabled "Wave-Out mix" / "Stereo Mix" / "Record What you hear".

Freecorder4, Replay Music, Replay AV, Replay Video Capture, Replay Media Catcher, Ask&Recorder Toolbar, WM Capture use a universal audio driver allowing you to record sound even on those computers that do NOT have a sound card!

You can also try other methods mentioned in the following thread:
Missing sound recording option "Stereo Mix" / "Record What you hear" / "Waveout mix"