I could draw some simple diagram using tikz -
\documentclass{article}
\usepackage{pgf}
\usepackage{tikz}
\usetikzlibrary{arrows,automata}
\begin{document}
\begin{tikzpicture}
% Axis
\draw (-0.5,0) -- (6.0,0);
\draw (0,-0.5) -- (0,3.0);
% Tasks
\node (rect) at (1,1) [draw,minimum height=0.65cm,minimum width=1cm] {$A$};
\node (rect) at (3,1) [draw,minimum height=0.65cm,minimum width=1cm] {$B_0$};
\node (rect) at (2,1) [draw,minimum height=0.65cm,minimum width=1cm] {$B_1$};
\node (rect) at (2,2) [draw,minimum height=0.65cm,minimum width=1cm] {$B_2$};
\node (rect) at (3,2) [draw,minimum height=0.65cm,minimum width=1cm] {$C_2$};
\node (rect) at (4,2) [draw,minimum height=0.65cm,minimum width=1cm] {$C_1$};
\node (rect) at (4,1) [draw,minimum height=0.65cm,minimum width=1cm] {$C_0$};
\node (rect) at (5,1) [draw,minimum height=0.65cm,minimum width=1cm] {$D_0$};
% Annotations
\node at (5.75,-0.25) {Time};
\node at (-0.35,1) {P1};
\node at (-0.35,2) {P2};
\end{tikzpicture}
\end{document}