I've gotten a basic export to Prosper working for a presentation I'm
writing to give this weekend.
Here is the extra portion for .emacs:
(setq org-export-latex-classes (cons '("prosper"
"% BEGIN Prosper Defaults
\\documentclass[pdf, contemporain]{prosper}
\\usepackage[utf8]{inputenc}
\\usepackage[T1]{fontenc}
\\usepackage[colorlinks,linkcolor=blue]{hyperref}
% END Prosper Defaults
"
("\\begin{slide}{%s}" . "\\begin{slide}{%s}"))
org-export-latex-classes))
Unfortunately it doesn't appear that I can add a closure for the
slide, so a manual "\end{slide}" must go at the end of each.