Why don't you just change locally the font to Times New Roman?

\documentclass[11pt]{book}
\begin{document}
Bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla.
\begin{center}\fontfamily{ptm}\fontsize{12pt}{14pt}\selectfont\bfseries
Two lines of centered text\\in Times New Roman 12pt
\end{center}
Bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla.
\end{document}
If you really need the system font Times New Roman, you can easily access it with XeLaTeX:
\documentclass[11pt]{book}
\usepackage{fontspec}
\begin{document}
Bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla.
\begin{center}\fontspec{Times New Roman}\fontsize{12pt}{14pt}\selectfont\bfseries
Two lines of centered text\\in Times New Roman 12pt
\end{center}
Bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla.
\end{document}
To use XeLaTeX, you may need to change a little your preamble (mainly things like \usepackage[...]{intputenc}) but everything which worked with dvips > ps2pdf should work with XeLaTeX.