I was recently surprised - and somewhat less than delighted at the nature of the issue - to be asked to fix a problem where the owner couldn't record a quick snippet of something that they were listening to, on an old Dell Inspiron 1300 lappy (complete with about 1 minute's worth of battery capacity!). The only options available were the line-in and mic. My heart sank as I wondered if it was going to be as tricky to 'record what you hear' as it was on my netbook with Linux Mint.
A quick search online revealed large numbers of complaints about Dell removing the feature to appease the recording industry. Oh dear. It looked like I was facing a challenge to get the SigmaTel audio working.
I thought forum threads like this one were going to be the answer.
I found a number of suggestions to add/change a registry key
I added a binary value “0000 01” and rebooted, but that didn't help.
The oft-given links for new R171789 drivers led to the "Sorry, not available" page on Dell's support site.
Finally, I found this link for the new drivers. The 1300 is listed in the compatibility list, so I downloaded and installed. The 1300 didn't appear in the installer list, but I pressed onwards, trusting the initial webpage more.
Success! We now have "SigmaTel Audio: Stereo Mix" in the drop down list in Audacity, and the owner can record what they need to, at last. Thank-you Dell, eventually :)
BTW you'll need to right-click the Systray volume icon, select "adjust audio properties", then select the audio tab, press the volume button on the Sound Recording section, and finally you'll arrive at the mixer panel where you can select the Stereo Mix as the recording channel. A bit of a longwinded route to get there, but at least you can!