Use the Debian package sndconfig to automatically identify your audio chip and to add this information to /etc/modutils/sndconfig.
If the audio device is not supported then you will probably need to get a newer kernel. Suppose you has an i810 audio chip (82801DB AC'97). Get this information from the lspci command:
$ lspci ... 00:1f.5 Multimedia audio controller: Intel Corp. 82801DB AC'97 ...
The PCI ID here is 82801. Look this up in /usr/src/linux/drivers/sound/i810_audio.c and if it's there, it should be supported.