You can use a minipage to achieve this along with a tabular. This method will not break across the pages though.
\documentclass{article}
\begin{document}
\begin{minipage}[l]{0.45\textwidth}
\begin{enumerate}
\item First item \\
This is the second line in item and this may extend to third if long
\item second item\ldots
\end{enumerate}
\end{minipage}%
\hfill
\begin{minipage}[r]{0.45\textwidth}
\begin{tabular}{|p{\textwidth}}
This is second part \\
$f(x) = 2x + 3y$ This line may go all along the end and wrap afterwards to the next as seen here\\
This is a forced next line by ending the previous line
\end{tabular}
\end{minipage}%
\end{document}

It seems the other possibility is with parallel package.
\documentclass{article}
\usepackage{parallel,enumitem}
\begin{document}
\noindent
Here we use \texttt{parallel} package.
\par
\begin{Parallel}[v]{0.48\textwidth}{0.48\textwidth}
\ParallelLText{\noindent
This is the left side.
\begin{enumerate}[itemsep=1ex,leftmargin=1cm,rightmargin=.52\textwidth]
\item { First item}
\item{second item}
\end{enumerate}
And you are back in business.\\
This list can break across pages automatically }
\ParallelRText{\noindent
This goes to the right. This may be going long. If you want you can input equations also.\\
$x=y+10$\\
This may be the best choice if you want this kind of thing to span multiple pages. }
\ParallelPar
\end{Parallel}
\end{document}

tabular, does that help? – doncherry Apr 27 '12 at 9:54