I've reccently accomplished task of developing own reporting system, which basically consist on design enviroment and data Source manager. The first task was to develop WYSWIG-like design enviroment. I've done this using GDI+, without even bothering about printing, as it came out printing/generating print preview was easiest than i expected, In general it only takes to draw all things on screen to graphics object of printing event.
I think that in case of WPF it would be similar, so all you should worry about is to display you report on screen and printing would be only few lines of code.
