I am pretty sure TikZ will make an entry here, since it is much more proficient and decorative with these things. However, it is possible using a combination of rules to obtain this layout. I decided to use an environment rather than two separate macros, since it seemed to be more fitting - an environment allows for a start and end declaration.

\documentclass{article}
\usepackage{showframe}% http://ctan.org/pkg/showframe
\newenvironment{separateA}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% left hang
\rule{\dimexpr\textwidth+.4in-.8pt}{.4pt}% horizontal rule
\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% right hang
}}}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% left hung
\rule[.5\baselineskip]{\dimexpr\textwidth+.4in-.8pt}{.4pt}% horizontal rule
\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% right hung
}}}
\newenvironment{separateB}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% left hang
\rule{\dimexpr\textwidth+.4in-.4pt}{.4pt}% horizontal rule
%\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% right hang
}}}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
%\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% left hung
\rule[.5\baselineskip]{\dimexpr\textwidth+.4in-.4pt}{.4pt}% horizontal rule
\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% right hung
}}}
\newenvironment{separateC}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
%\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% left hang
\rule{\dimexpr\textwidth+.4in-.4pt}{.4pt}% horizontal rule
\rule[-.25\baselineskip]{.4pt}{\dimexpr.25\baselineskip+.4pt}% right hang
}}}
{\par\nobreak%
\noindent\smash{\makebox[\textwidth]{%
\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% left hung
\rule[.5\baselineskip]{\dimexpr\textwidth+.4in-.4pt}{.4pt}% horizontal rule
%\rule[.5\baselineskip]{.4pt}{.25\baselineskip}% right hung
}}}
\begin{document}
Some fully boxed text, using \verb|separateA|:
\begin{separateA}
Here is text in the frame.
\end{separateA}
Some partially boxed text (left and right), using \verb|separateB|:
\begin{separateB}
Here is text in the frame.
\end{separateB}
Some partially boxed text (right and left), using \verb|separateC|:
\begin{separateC}
Here is text in the frame.
\end{separateC}
Here is concluding text.
\end{document}
The above MWE provides three environments, for the sake of difference (although they're virtually identical): separateA prints a "fully boxed" block, while separateB prints a "partially boxed" block (left and right) and separateC also a "partially boxed" block (right to left). Care is taken to make the horizontal separation be exactly \textblock+.4in wide, hanging over the edge by exactly .2in on either side.
It would be easy to construct a single environment (say) separate to do this, with optional arguments for control over the placements of the hangs/hungs.
showframe was used to highlight the text block boundary, and indicate and accentuate the overhang outside the text margin.
mdframed-example-default.pdf– Marco Daniel Mar 03 '12 at 19:06