Minimal example of XeLaTeX with Velthuis input mapping

\documentclass{article}

\usepackage{polyglossia}

\newfontfamily
  \sanskritfont [Script=Devanagari,Mapping=velthuis-sanskrit]{Sanskrit 2003}

\begin{document}

\sanskritfont
\noindent\huge

aasiidraajaa nalo naama viirasenasuto balii|\\
upapannairgu.nairi.s.tai ruupavaana"svakovida.h||

\end{document}