Here is a solution using titlesec
, titletoc
and fmtcount
, plus the \rmntonum
command from etoolbox
; we have to use it to convert the way part numbers appear in the .aux file (Roman numerals) to arabic.
\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{fourier}
\usepackage{microtype}
\usepackage{babel}
\usepackage{lipsum}
\usepackage{etoolbox}
\usepackage{fmtcount}
\usepackage[pagestyles, newparttoc]{titlesec}
\titleformat{\section}[hang]{\large\bfseries\boldmath}{§~\thesection}{0.6em}{\itshape}%
\titleformat{\part}[block]{\filcenter\lsstyle\bfseries\scshape\Large}{ \Ordinalstring{part} \partname: }{0.5em}{}%
\usepackage{titletoc}
\dottedcontents{section}[4em]{\bfseries}{1.85em}{1pc}%
\newsavebox{\partlabel}
\titlecontents{part}[1.5em]{\medskip\bfseries\renewcommand{\thepart}{\relax}}%
{\sbox{\partlabel}{\Ordinalstringnum{\expandafter\rmntonum\expandafter{\thecontentslabel}}~\partname: }%
\contentslabel[\usebox{\partlabel}]{0em}\hphantom{[\usebox{\partlabel}}}%
{\hspace*{0.06em}}%
{\hfill\contentspage}%
[\smallskip]%
\begin{document}
\tableofcontents{}
\part{An Interesting Part}
\lipsum[1-2]
\section{A First Section}
\lipsum[1-10]
\section{A Second Section}
\lipsum[1-10]
\part*{A Boring Numberless Part}
\lipsum[1]
\section{Section A}
\lipsum[1]
\section{Section B}
\lipsum[1]
\part{Another Numbered Part}
\end{document}

\part
in the document?\part{The title}
should give you "First part: The title" both in the ToC and in the document (as in my answer) or is it something else what you are trying to achieve?