Your Google source is wrong.
The PDF version of LaTeX pdflatex
supports the PNG format out of the box, including transparent PNGs. If you have your logo in another format like GIF than simply convert it to PNG first. I would not recommend to use the normal latex
compiler with DVI output.
You need the standard package graphicx
to include the image. Loaded xcolor
would also be a good idea.
Here some examples which use a transparent test PNG I got from http://entropymine.com/jason/testbed/pngtrans/rgba16.png.
\documentclass{article}
\usepackage{xcolor}
\usepackage{graphicx}
\begin{document}
\framebox{\includegraphics{rgba16.png}}
\colorbox{red}{\includegraphics{rgba16.png}}
\colorbox{white}{\includegraphics{rgba16.png}}
\colorbox{yellow}{\includegraphics{rgba16.png}}
\end{document}
The first image shown is the original transparent PNG. As you can see the other work fine with some background color.

For advanced effects like patterns and shadings I would recommend you PGF/TikZ (i.e. the tikz
package).
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{patterns}
\begin{document}
\begin{tikzpicture}
\node [pattern=north east lines,inner sep=10pt] {\includegraphics{rgba16.png}};
\end{tikzpicture}
\begin{tikzpicture}
\node [shade,left color=yellow,right color=blue,inner sep=10pt] {\includegraphics{rgba16.png}};
\end{tikzpicture}
\end{document}

beamerposter
.