Compaq have many model that equipped with certain manufactures audio components. From my experience working with Compaq/HP, there are 3 major type of AUDIO component they use which is REALTEK, IDT - high definition audio devices and conexant.
The problems occurred When Windows Vista arrived, many laptop such as CQ40 and CQ35 model have problems with windows XP installation and installig the Driver especially AUDIO. However i have write posts to solve the problems which you may refer here:
Slipstreaming Guide To install Windows XP
Slipstreaming guide here is a method for those who do not have external floppy drive. And for those who have the external floppy drive may install the XP directly without the slipstreaming process.
For the Audio especially for compaq CQ40 and CQ35 (may also work with vista bae model which use IDT),
I write 2 post how to install the audio driver:
General Audio Installation
and for those who have problems with audio disappear after restart this poost may help you.
Hope this article help and if you have any question feel free to leave your comments.