[pdftex] figures side-by-side?

[E. Kristina Brock]

Hi I am trying to include figures side-by-side.  I thought I could use
minipage to do this, but it won't compile, saying I have a missing number
or something, which doesn't really make sense to me.

This is what I tried:
\begin{figure}[htb!]
\begin{minipage}[t][3.5cm]
\includegraphics[scale = 0.75, viewport = 10cm 17cm 10cm
22cm]{./figs/powerpole}
\end{minipage}
\begin{minipage}[t][3.5cm]
\includegraphics[scale = 0.75, viewport = 10cm 17cm 10cm
22cm]{./figs/powerpole2}
\end{minipage}
\caption{average dynamic model}
\label{avgpowerpole}
\end{figure}

Now, on another note, the viewport command seems strange to me also, so I
have just been modifying the numbers that are supposed to correspond to
llx lly urx ury by trial and error until it looks right.  Does it seem
impossible that my llx and urx are the same?

Please help if you can!

Thanks