Aligning paragraph inside a tabular

Due to technical reasons (or let's say bidirectional typesetting bugs of XeTeX), you need to put list-like environment inside \parbox or minipage environment. Therefore the solution is:

\documentclass{article}
\usepackage{bidi}
\setRTL
\begin{document}

\begin{tabular}{|p{5cm}|}
  \hline
  \textbf{item 1:} These are some texts to just fill in the first line.
   \tabularnewline
   this is the second Item which still needs to be indented
\parbox{5cm}{\leavevmode%
   \begin{itemize}
    \item item 1
\item item 2
   \end{itemize}}
 \\ \hline 
\end{tabular}

\end{document}

or

\documentclass{article}
\usepackage{bidi}
\setRTL
\begin{document}

\begin{tabular}{|p{5cm}|}
  \hline
  \textbf{item 1:} These are some texts to just fill in the first line.
   \tabularnewline
   this is the second Item which still needs to be indented
\begin{minipage}{5cm}
   \begin{itemize}
    \item item 1
\item item 2
   \end{itemize}
\end{minipage}
 \\ \hline 
\end{tabular}

\end{document}

Are you after something like this?:

\documentclass[a5paper]{article}
\usepackage{tabularx}
\begin{document}
\begin{tabularx}{\textwidth}{|>{\bfseries}lX|}
  \hline
  Item 1:& These are some texts 
  just to fill in the first line. 
  And some more texts 
  just to fill in the second line.\\
  Item 2:& These are some texts 
  just to fill in the first line. 
  And some more texts 
  just to fill in the second line.
 \\ \hline 
\end{tabularx}
\end{document}​

---

Updated, in the light of more detail in the question:

\documentclass[a5paper]{article}
\usepackage{tabularx}
\begin{document}
\begin{tabularx}{\textwidth}{|>{\bfseries}lX|}
  \hline
  Item 1:& These are some texts 
  just to fill in the first line. 
  And some more texts 
  just to fill in the second line.\\
  & This is the second Item which still needs to be indented
\begin{itemize}
\item item 1
\item item 2
\end{itemize}
\\ \hline 
\end{tabularx}
\end{document}​

Note that: (a) I've made the major item stub a separate column in the table (Sorry, I don't know whow tabularx works with RTL text); and (b) rather than \tabularnewline, I've added a table row for the second bit. Although this may not match what you're doing syntactically, I think it might make things a bit more maintainable.

---

This is how I guess RTL might work:

\documentclass[a5paper]{article}
\usepackage{tabularx}
\begin{document}
\begin{tabularx}{\textwidth}{|X>{\bfseries}l|}
  \hline
 These are some texts & Item 1: 
  just to fill in the first line. 
  And some more texts 
  just to fill in the second line.\\
  This is the second Item which still needs to be indented
\begin{itemize}
\item item 1
\item item 2
\end{itemize}
\\ \hline 
\end{tabularx}
\end{document}​