Gateway "Stereo Mix" in Windows Vista.!!! ( Give me Help pleases )

[hi________]

Hi all ~

I am a new member here , my problem is about "Stereo Mix'' in my Windows Vista Gateway computer ~

I have follow this step to find my Stereo Mix : Control Panel --> Sounds --> Recording Tab --> Right click on the white area, and select "show disable devices"

But my Stereo Mix didn't show up , i cant find Stereo Mix ~
I am giveup , i have no idea with this , that is why i am here to post my problem ~

MY Gateway Computer model is : Gateway GM5454E

I dont know what is next i can do , I wanna help , pleases ~
I hope any one can got me , waiting for reply..............................