\documentclass{article}
\usepackage{pstricks}
\pagestyle{empty}
\parindent=0pt
%
\newsavebox\pstBox
\newlength\pstWidth
\newlength\pstHeight
\makeatletter
\def\psLBox{\@ifnextchar[{\psLBox@i}{\psLBox[]}}
\def\psLBox@i[#1]#2{%
  \psset{linearc=0.4,shadow=true,shadowsize=0.2,%
      fillstyle=solid,fillcolor=white}
  \ifx#1\empty\else\psset{#1}\fi
  \sbox\pstBox{#2}
  \pstWidth=\wd\pstBox
  \pstHeight=\ht\pstBox
  \advance\pstHeight by \dp\pstBox
  \advance\pstHeight by \pslinearc
  \advance\pstWidth by \pslinearc
  \begin{pspicture}(\pstWidth,\pstHeight)
    \psline(\pstWidth,0)(0,0)(0,\pstHeight)(\pstWidth,\pstHeight)%
    \psline[shadow=false](\pstWidth,\pstHeight)(\pstWidth,0)
    \rput(0.5\pstWidth,0.5\pstHeight){#2}
  \end{pspicture}
}
\makeatother
\newlength\postercolwidth
\setlength\postercolwidth{0.3\textwidth}
\newpsstyle{boxstyle}{framearc=0.2,fillstyle=solid,fillcolor=black!15,framesep=4mm}
\newsavebox\PBox
\def\myBox#1#2#3{%
 \sbox\PBox{\psframebox[style=boxstyle]{\parbox{#1}{#3}}}%
 \begin{pspicture}(0,-\ht\PBox)(\wd\PBox,1.2\ht\PBox)%\psgrid
   \rput[l](0,0){\usebox\PBox}
   \rput[l](5\fboxsep,\ht\PBox){\colorbox{yellow}{#2\hspace{\fboxsep}}}
 \end{pspicture}%
}
\parindent=0pt
\begin{document}

\hspace{10mm}\myBox{\postercolwidth}{\Large Abstract}{%
   Lorem ipsum dolor sit amet, urna augue. Luctus sollicitudin,
   accusantium nostrum. Scelerisque duis eget nonummy, rhoncus}
%
\hspace{10mm}\myBox{\postercolwidth}{\Large Abstract}{%
   Lorem ipsum dolor sit amet, urna augue. Luctus sollicitudin,
   accusantium nostrum. Scelerisque duis eget nonummy, rhoncus
   Lorem ipsum dolor sit amet, urna augue. Luctus sollicitudin,
   accusantium nostrum. Scelerisque duis eget nonummy, rhoncus}

\bigskip
\psLBox{Some text in a box}
\psLBox[fillcolor=lightgray]{%
\parbox{3cm}{Some text in a box with linearcs only 
    on the left side}
}% 

\end{document}