Got a Dell laptop and with the SigmaTel sound chipset and stuck with all it’s advanced features such as lack of stereo mix? Dont worry, a solution is here. 

Note: The solution below no longer applies as Dell have finally released a driver update supporting Stereo Mix. Check the Drivers and Downloads section of the Techincal Support on Dell’s website then use the appropriate utilities to locate the new driver.
The drivers release date is marked as the 12/4/2007, v.5.10.0.5515_Rc22, try this direct download link: R171789.exe

Firstly install the Dell SigmaTel drivers, then simply go to http://au.lge.com/support/software.jsp then set the Product field to Notebook, leave the Series to All, Choose your OS and set it accordingly then make the subject SigmaTel. You should get three results , you want [Sound/2000/XP] SigmaTel Sound Driver Ver 5.10.0.4866 XNOTE(LE50). Download this driver and install it to get Stereo Mix on the SigmaTel chipset. Simple :-)