\documentclass[a4,12pt]{seminar}

\usepackage{pstcol} % To use the standard `color' package with Seminar
\usepackage{semcolor}
\usepackage{semlayer}
\input{seminar.bug}

\begin{document}

\begin{slide}
  \centerline{\psshadowbox{\shortstack[l]{%
    The winner is: \begin{overlay}{1}{\textcolor{red}{Caroline}}\end{overlay}\\[2cm]
    The second is: \begin{overlay}{2}{Jane}\end{overlay}\\[2cm]
    The third  is: \begin{overlay}{3}{Mary}\end{overlay}}}}
\end{slide}

\end{document}

