Sub Articulo 120.1

\@addtoreset is your friend.
Yours sincererly
  Heiko 
PS: Your example rewritten:
\documentclass[dvips,12pt]{article}
\usepackage[colorlinks]{hyperref}
\usepackage{graphicx}
\renewcommand{\theequation}{\thesection.\arabic{equation}}
\renewcommand{\thefigure}{\thesection.\arabic{figure}}
\makeatletter
\@addtoreset{equation}{section}
\@addtoreset{figure}{section}
\makeatother
\begin{document}
\section{first section}
\begin{figure}
  \centering
  \includegraphics{fig-a}
  \caption{figure a.}
  \label{fig:fig-a}
\end{figure}
Hello World
\section{second section}
\begin{figure}
  \centering
  \includegraphics{fig-b}
  \caption{figure b.}
  \label{fig:fig-b}
\end{figure}
In figure \ref{fig:fig-b}, you see that...
\end{document}