\documentstyle{article}

\newlength{\indentmargin}
\setlength{\indentmargin}{1in}		% this is the size of the indentation

\newlength{\indentwidth}
\setlength{\indentwidth}{\textwidth}
\addtolength{\indentwidth}{-\indentmargin}

\begin{document}

This is some text that is not indented. It runs to the margin.  I
personally promise it does.  No, really.  And it should fill a line up.
\strut\par
\noindent\hspace{\indentmargin}\parbox{\indentwidth}{
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
Is this text indented by 1in?
How about this?
}

\end{document}