inspiron 1525 stereo mix problem

i have window vista x-32, inspiron 1525

and i want to get stereo mix, but it wasn't there.

 1. intel(r) high definiton audio HDMI

 2. SigmaTel High definition Audio codec

that are the ones are listed in the device manager.

There was a driver for win vista x-32 and inspiron 1525,

"SIGMATEL STAC 92XX C-Major HD Audio"

so i downloaded but nothing happen.

do i have to get the sound card?