\documentclass[a4paper,draft]{article} 

\usepackage[Greek,Latin]{ucharclasses}
\usepackage{xltxtra}
\usepackage{xgreek}
\setTransitionsForGreek{\setlanguage{greek}}{\setlanguage{american}}
\setmainfont[Mapping=tex-text]{Times New Roman}

\begin{document}

\end{document}