If I use mouthwash, do I still need to floss?

Yes. Mouthwash may kill some of the bacteria present in your mouth, but not all. You need to get rid of the crud that stays in between your teeth near the gum line - it's called plaque. Instead of the nuisance of flossing, you could use a dental pick - they're available at any pharmacy, and are much easier to use. Pick first, brush your teeth second, and don't rinse after the final "spit-out". That way, the fluoride in the toothpaste has a chance to work longer. (Recommended by my dentist.)