If you have Windows Vista and Sigmatel Audio Card and not getting the stereo mix option under recording settings.
Please modify following settings.
1 Uninstall the previous drivers
2 Disable UAC
3 Download these drivers http://ftp.us.dell.com/audio/R171789.exe
4 Restart and right click on drivers and click on compatibility tab and make sure its selected to (Run in Windows xp Mode).
5 Install Audio Drivers
6 Restart again and in control panel now you should have Stereo mix options under recording.