ITunes Won't Download?

Yesterday I deleted some programs I felt weren't necessary because there was a virus (now gone) and I wanted to clear space on my computer. I deleted some files I shouldn't have, including "Bonjour" and "Apple Application Support". I'm not a computer whiz, I didn't realize that these programs were necessary to run iTunes, and now I can't open iTunes. I tried finding a place on the internet I could re-download Apple Application Support, and I haven't yet. What should I do?