How do I found out my motherboard model number to

Compaq's use a product number to identify what is inside.
That number is on a label on the outside of the computer usually on the back.

Using that number and the model on the Compaq web site (support section) will direct you to the drivers you want.

This is of course provided you have not added a separate sound card in which case you should go direct to the sound card site eg Creative Labs.