\documentclass{article} 
\usepackage{c:/Programme/R/R-2.10.0beta/share/texmf/Sweave}
\usepackage[latin1]{inputenc}
%\usepackage[utf8x]{inputenc}
\usepackage[german]{babel}

\begin{document}
<<>>=
Umlaute <- c("ä","ö","ü","ß")
Umlaute
@
\end{document}
