A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Have a look here:
http://www.pptfaq.com/FAQ00052.htm
You won't be able to get the resolution you're after, though. PPT won't export images at over 3072 pixels.
That translates into 300dpi at around 10" max.
There are better ways of printing posters though.