\documentclass[a4paper,12pt]{report}
\usepackage{ifthen}
\begin{document}

\newsavebox{\kasten}
\sbox{\kasten}{\fbox{\rule{0mm}{1em}\hspace{1ex}}}
\newcounter{i}
\newcommand{\zeile}[1]
{\setcounter{i}{0}
 \whiledo{\value{i}<#1}
   {\usebox{\kasten}\stepcounter{i}}}

\centerline{\underline{\bf Anmeldung}}
\vspace*{1em}\noindent
\makebox[2cm][l]{Name} \zeile{15}\\[.5ex]
\makebox[2cm][l]{Anschrift} \zeile{20}\\[.5ex]
\makebox[2cm][l]{Telefon} \zeile{15}

\end{document}