See <http://tex.stackexchange.com/questions/4178/>

odd-two-col.tex

\documentclass{article}
\usepackage{framed,lipsum}
\newlength\colsize
\newlength\figcolsize
\setlength\colsize{8cm}
\setlength\figcolsize{8cm}
\newenvironment{twocol}{%
  \def\FrameCommand##1{%
    \hspace{-10cm}
    ##1%
  }
  \begin{MakeFramed}{%
    \setlength\hsize{\colsize}%
  }
}{%
  \end{MakeFramed}%
}
\newcommand\marginfig[2][0pt]{%
  \leavevmode
  \smash{\makebox[0pt][l]{%
    \hspace{\dimexpr(-\parindent+\colsize+\marginparsep)}%
    \raisebox
      {\dimexpr(#1+\baselineskip-\height)}
      {\parbox{\figcolsize}{\centering #2}}%
  }}%
}
\begin{document}
\lipsum[1-3]
\begin{twocol}
\lipsum[10]
\marginfig{\leftarrowfill figure column size is this big \rightarrowfill}
\lipsum[11]
\marginfig{\fbox{\rule{3cm}{3cm}}}
\lipsum[12]
\marginfig[-2cm]{\fbox{\fbox{\rule{2cm}{2cm}}}}
\lipsum[13-14]
\end{twocol}
\lipsum[20]
\end{document}