\includegraphics[scale=0.2]{higgs_potential3.pdf}

----------------------------------------------------
\begin{figure}[t]
\begin{center}
%\scalebox{1}[1]{
\includegraphics[scale=0.25]{s-t-plot.pdf}
%}\\
\end{center}
\caption{text}
\end{figure}

----------------------------------------------------

- \usepackage{graphicx} or \usepackage{graphics} is necessary
- under PDFLaTeX ".ps" and ".eps" formats do not work
  - might be fixed (not all of this works under older versions of LaTeX):
    put "\DeclareGraphicsExtensions{.eps}" after \begin{document}
  - for alternative solutions of the problem, see e.g.
    http://www.trevorrow.com/oztex/ozfaq.html#pdfeps