\documentclass[letterpaper,11pt,twoside]{article}

\usepackage{pstricks}


\begin{document}
\begin{figure}
{
\centering
\begin{pspicture*}(0,0)(10,10)
\psline[linecolor=red]{->}(2.3,1)(7.8,1)   % horizontal
\psline[linecolor=blue]{->}(2,1.8)(8,8.2)  % diagonal
%
\rput(5,1.5){\small Horizontal}
\rput{47}(4.7,5.4){\small Diagonal}
\end{pspicture*}
\caption{Some caption}\label{fig:somefig}
}
\end{figure}

\end{document}