You may need to enable a module or include it in a new compilation of your kernel.
I suggest upgrading to the newest kernel version.
EDIT: (You say you have 2.6, but you weren't more specific. It's up to 2.6.11.7 now.)
http://www.freeos.com/articles/2589/
Make sure you configure it, and include modules that are needed to support your sound card.
And if the kernel just doesn't support your sound card (it should), then you need to hit up google for Linux-compatible drivers for that sound card.