Using iTunes On A New Computer?

I recently bought a new computer and I want to use it to sync my iPhone with iTunes. I copied all of my music from my old computer and put it in iTunes on my new computer. I also signed in to my iTunes account on my new computer. Here's the problem:

When I try to sync it basically says "all of your data will be erased." Now I don't mind if my music gets erased because I have copied these items, but will all of my apps be erased? I know I could just re-download them but none of my settings/preferences/data will no longer be on them. Is there an easy way I can sync with my new iTunes without deleting all of my apps/photos?

It should be simply overwriting a copy of the same song in order to preserve space.