Hello Natayla-

Yes, you need a sound card in order to have sound, regardless of whether you
have Vista, Windows XP, OS X, or Linux.  Without a sound card, you would have
nothing to plug your speakers into.  That having been said, I have not seen a
computer without a sound card... well... ever.  Even the cheapest computer
should have built in sound on the motherboard.  If you have a jack to plug
speakers in, then you have a sound card.

-Sean