I recently reformatted my 1526, and found that the default windows driver for the mic jack in the front and also the built-in microphone, didn't work. Not having easy access to the dell discs that   I looked up my laptop in the drivers section and downloaded the R170217 that is recommended for the 1525, and 1526's running vista 32-bit.  When trying to install this driver package I received the error message:

"This is not the correct audio driver for this system. The installer will now exit"

After searching the dell forums, which gave me no useful insight, I ended up fumbling through IDT's(The company that bought Sigmatel) website along with outside tech forums. I determined that indeed, this is the wrong driver for this laptop running this operating system.  I'm running Vista Home Premium 32-bit.

Here is the audio driver that works for me with the sigmatel stac 92xx c-major hd audio for the Dell Inspiron 1526 laptop:  R166861