On a Mac (pdftex) I managed to include a png file simply with \includegraphics[width=1.2\textwidth]{filename.png}. But in order for that to work I had to comment out the following 2 packages:
%\usepackage[dvips]{epsfig}
%\usepackage[dvips]{graphicx}
...and simply use package graphicx:
\usepackage{graphicx}
It seems [dvips] is problematic when used with pdftex.