It will be easier to show you. Click the link:
http://www.overclockeddoc.com/bookwo...0io%20slot.JPG
Look at the back of this tower.
If you have integrated sound your speakers will plug into the IO plate as labeled in the picture.
If you have a sound card, your speakers will plug into ports down in the expansion slots.
A sound card would most likely solve your problem. Generally, decent sound cards sound better than integrated audio, and save CPU cycles as well. Which makes your computer run a little quicker.