After seeing a lot of threads in different forums and trying myself, finally my laptop has sound.

Previously, Realtek 268 was not officially support and people in Ubuntu Forum used patches together with the recently released ALSA drivers to fix this problem, more details in here: https://bugs.launchpad.net/ubuntu/+source/linux-source-2.6.22/+bug/116326

However, OSS and ALSA are misplaced and can not worked in some programs (for example, no system sound and no TTS in Stardict) under this setting.

Now, in the official website of Realtek, they released the most updated drivers on Augest 20th and it works well. You can hear the system sound as well as TTS in Stardict.

The last problem is about the microphone. If you want to use Audacity to record the voice, then install alsa-oss http://gd.tuwien.ac.at/opsys/linux/alsa/oss-lib/alsa-oss-1.0.12.tar.bz2
It seems that Audacity will only work under OSS scheme.

This solution is useful for Acer Travelmate 6292/6231 and some other laptops with Realtek 268 codes.