Unpack it but cancel the installation process.
It will unpack the files and store them in a folder on the hard drive at c:\Dell\drivers\R99254, and that folder will have a subfolder named WDM.
Open Device Manager and expand System devices near the bottom. Find the PCI Device entry with a ? next to it (or if that is not there then look for "Multimedia Audio Controller") . Go to the properties and choose to update the driver. Choose to manually find the driver and don't let Windows look for it. Browse to c:\Dell\drivers\R99254\WDM
Reboot and it should detect some new hardware and one of them should be the Sigmatel.