Look at the back of your computer where all the wires plug in.
Is there anything that looks like this?
http://static.howstuffworks.com/gif/sound-card-soundblaster.gif

Only the metal plate will be showing, the rest of the card is inside the
computer's case, and can't be seen unless you take off the cover.

The round holes are where you plug in speakers, microphone, headset, etc.
If there's nothing like that, then I'd say you don't have a sound card.