\documentclass[a4paper,ngerman,12pt]{article} 
\usepackage[T1]{fontenc} 
\usepackage[utf8]{inputenc} 
\usepackage{SIunits}
\usepackage{array}
\usepackage{dcolumn}
\usepackage{booktabs}
\usepackage{babel}
\setlength\parindent{0pt}% damit nicht eingerueckt wird

\makeatletter
\newcolumntype{n}{l}
\newcolumntype{N}{>{\scriptsize}l}
\newcolumntype{d}[1]{>{\DC@{.}{,}{#1}}l<{\DC@end}}
\newcolumntype{v}[1]{>{\raggedright\hspace{0pt}}p{#1}}
\newcolumntype{V}[1]{>{\scriptsize\raggedright\hspace{0pt}}p{#1}}
\makeatother

\begin{document} 

\begin{tabular}{@{}n*{4}{d{4.0}}@{}}\toprule% tab11.tex
  \multicolumn{1}{@{}N}{Monat} & \multicolumn{2}{N}{Frauen} & \multicolumn{2}{N@{}}{Männer} \\
      \cmidrule(lr){2-3}\cmidrule(l){4-5}
& \multicolumn{1}{N}{1967} & \multicolumn{1}{N}{1968} & 
  \multicolumn{1}{N}{1967} & \multicolumn{1}{N@{}}{1968} \\
      \cmidrule(r){1-1}\cmidrule(lr){2-2}\cmidrule(lr){3-3}\cmidrule(lr){4-4}\cmidrule(l){5-5}
 September & 2000 & 1700 & 2300 & 1900 \\
 Oktober   & 1500 & 1800 & 1900 & 3000 \\
 November  & 2500 & 2800 & 4700 & 3200 \\
 Dezember  & 2300 & 2000 & 3600 & 2700 \\\bottomrule
\end{tabular}

\end{document}
