\documentclass[12pt]{article}% Hebrert Voss - 20030813
% --- for a solution with tabls.sty
\usepackage{tabls}
\makeatletter
\newcommand\atbottom[1]{%
  {\divide\@arstdepth\normalbaselineskip % number of full lines
   \multiply\@arstdepth\normalbaselineskip % distance rounded down to lines
   \lower\@arstdepth\hbox{#1}}}
\makeatother
% ---
\parindent=0pt
\begin{document}

\section*{Solution with \texttt{tabls.sty}}
There are different problems with the \verb|tabls| package, which doesn't work
with some other packages.


\vspace{0.5cm}
\begin{tabular}{|l|p{2in}|l|l|}\hline
1. & Blah blah blah blah blah blah blah blah blah.
     Blah blah blah blah blah blah blah blah blah. &
          \atbottom{xx1} & At top \\
\hline
\end{tabular}

\section*{Solution without any package}
This works only when the cell with the bottom allignement is the last one.

\vspace{0.5cm}
\newlength{\negskip}
\setlength{\negskip}{-\baselineskip}
\addtolength{\negskip}{-\lineskip}
\begin{tabular}{|l|p{4cm}|l|}\hline
A  & B & C\\\hline
1.
  & Blabla bla bla bla\newline
    bla bla bla bla bla\newline
	bla bla.
  & \mbox{}\\[\negskip]
  &  & xxx1\\\hline
2.
  & Blabla bla bla bla\newline
	bla bla.
  & \mbox{}\\[\negskip]
  &  & xxx2\\\hline
\end{tabular}

\end{document}