Hi,
I am looking for an application on the iPhone, where I can browse through picture structures with, select single pictures and zoom into details.

I would like to use the iphone as a platform to put hires jpg pictures from my nikon onto the iphone, select them, show / zoom and discuss details with my friends at work.

Is there already any application that supports these kind of functions?

well, yeah. If you take the pictures form your nikon and put onto your computer, make a folder with all of the pictures you want somewhere. Go to iTunes, click on the iPhone in the sidebar, click the Photos tab, then find the folder with the pictures you want and press apply. iTunes will then sync all of the photos to iPhone and you can view them by clicking Photos then tapping Photo Library.