Debian squeeze comes with Alsa drivers 1.0.21 by default:
and you’ll see which version you have installed. Unfortunately my Sony Vaio needs Alsa 1.0.23 to work. Debian Squeeze has alsa-source for 1.0.23 in the repository, so it’s only a question to go into a terminal and use module assistant.
m-a a-i alsa
an ncurses screen will show up while compiling the sources. Just restart and verify that you have the new version.