will all my current pictures on the ipod get erased?

I bought a Macbook air a few months back and downloaded photos to iPhoto from my iphone. A couple of days back, i was attempting to download the photo library i have in my classic ipod to the macbook air. A message stating: " Are you sure you want to remove existing photos and sync photos from this computer" appeared. having said that, i need help in uploading the photos on my iphoto library to the classic ipod without erasing the existing files.

How do I get there? should i find a way to download the files to the laptop first then sync all files back to the ipod?