yep. The airconditioning compressor is hanging off the side off the side of your block underneath the powersteering.
When you look at the belt, you'll see that it goes around the crank, the airconditiong compressor, and a pulley. The puley is the adjuster, and moves up and down so that the circumference of the belt (and hence tension is changed). You loosen the bolt at the back of the adjuster pulley, and the one that is screwed in from the bottom adjusts the pulley up and down, - hence tension.
Depending on the age of the belt I would probably just replace it. If you don't know when it was last changed, then just change it. Will only cost you about $20. Even if you tighten the belt, once the polyrib belts start slipping (squealing sound) they glaze over a little, and are even more prone to slipping again.