If a pair of floats are to be forced to form a 2-page spread (in a book, or whatever), the first must lie on the left side of the spread, on an even-numbered page. The dpfloat package provides for this: the construction to use is:
\begin{figure}[p]
\begin{leftfullpage}
<left side figure>
\end{leftfullpage}
\end{figure}
\begin{figure}[p]
\begin{fullpage}
<right side figure>
\end{fullpage}
\end{figure}
The construction has no effect unless the standard class option
twoside is in effect.
Full documentation of the package (such as it is) is to be found in README.dpfloat
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=dpfloat