To find out what onboard sound device you have:
If it is a brand-name computer (i.e. Dell, HP, etc.) - I would advise going to the company's website under their support section, looking up your make/model of computer (i.e. Dimension 4500, Pavilion xf335, etc.) for its specs. Dell even has it where you can put in the service tag and download the driver from that (there may be a couple of different ones for each service tag - it doesn't hurt to use trial and error - just use the Add/Remove Programs to find what you installed that doesn't work and remove it from there before trying another (and reboot as prompted), so pay attention to the name it installs as (i.e. SoundMAX Audio, etc.).)
If you have a computer built from parts - consult your motherboard manual for what chip number/chipset your audio device has and use my link from my earlier post to download the driver. If you don't have the manual, but have the box, google the model of the motherboard to find out the sound device. If you have neither box, manual, and the board has no distinguishing marks to say what model it or your sound is, or you just can't see them, then I would recommend to get a PC auditing program that can tell you what your hardware is. AIDA32 is a good one (
http://www.sofotex.com/AIDA32-download_L9326.html), Belarc Advisor (belarc.com) is another.
Good luck.