In order to get the onboard AC97 sound working from Hard disk install, you will have to do the correct installation. As U are aware that if U boot from CD using "knoppix alsa" at booth prompt, that sound works fine. So U boot from CD using "knoppix alsa" and then do the HD installation. U can also make the Boot floppy during install and then U will find that sound will work even from HD install.
I have got that working last night.