\documentclass[11pt]{letter}
\usepackage{geometry}
\geometry{a4paper}
\usepackage{graphicx}
\usepackage{textcomp}
\usepackage[greek,frenchb]{babel}
\usepackage{amssymb}
\usepackage{epstopdf}
\usepackage{wrapfig}
\DeclareGraphicsRule{.tif}{png}{.png}{`convert #1 `dirname #1`/`basename #1 .tif`.png}
\begin{document}
\begin{flushright}lieu, la (date) 2009\\
\end{flushright}
blah blah blah
\begin{figure}[h!]
\includegraphics[width=3in]{presentation}
\end{figure}
\end{document}
---------------------------
The error is ...
Underfull \hbox (badness 10000) in paragraph at lines 16--18
! LaTeX Error: Environment figure undefined.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.19 \begin{figure}
[h!]
?
There's no figure environment in the letter class. You probably
want to change it into a center or flushleft environment.
It's not necessary to put an \includegraphics command into a
figure environment, it may go everywhere (sometimes, though,
it needs to be preceded by \protect, not in this case).
Ciao
Enrico
The letter document class is designed for letters. Since letters
typically don't have figures in them, the `figure' environment is not
defined. You don't need to use the figure environment to include an
image. Just remove the \begin{figure} and \end{figure} commands and
it will compile fine.
As an aside, you may want to have a look at the documentation for the
letter document class. You don't need the flushright environment to
put the date on and you generally start a new letter with \begin
{letter}{Addressee} some time after \begin{document}; you can then use
\date{....} and it'll appear in the right place.