This worked for me on my Compaq C751 with XP SP2 :
SP37816 Conexant HD-Audio SmartAudio 221 v. 18.104.22.168 drivers from
(same as above)
Using these instructions:
" choose the "Don't search. I will choose the driver to install" option, and then clicking the "Have Disk" button, and browsing in the list down to "Sound and Audio Devices" and browsing to the sound card driver folder from there.
Windows will kick and scream at you because you're basically forcing it to use a driver that it thinks is wrong, but my sound card now works perfectly!!