Im new into that asp.net thing, but here goes.
I got at ImageButton, and when its clicked i want the image displayed in another window. If I can avoid using ajax i would like to do that. If possible would like to make the window modal, but still avoid ajax, since Im not ready to mix more technolgies yet.
IMHO the best practice to show a picture is in the same page on the top of the content. I personally use Lightbox. You can find the documentation on their page, so it should be easy for you to integrate their JavaScript code.