Finally, I am able to make it work. So how it happened?
I downloaded the driver for sound card for Windows 7 from HP website and just went thru its INF file to check out what exactly the sound card is. There I found, the sound card is
So my problem before was that I was searching for "Conexant High Definition Audio Device driver" and not "Conexant Function Driver for Pebble High Definition Audio Device".INF file for installing the Conexant Function Driver for Pebble High Definition Audio Device
This all made the difference and hence all the drivers were not working. So finally when i searched for Conexant Function Driver for Pebble High Definition Audio Device, I got a driver uploaded or modified by someone on Skydrive.
After Installing this driver manually and a reboot, all is working great. Thanks to the guy who uploaded it. It would be great if HP could make it officially available.