[pstricks] Silly question abou pspicture... sorry

[Pedro Jorge Caridade]

Hi all
Since I need to import some pstricks graphics into flash and keep track 
of the initial (pstricks) coordinates, I need to create a pspicture with 
some fixed size. This part is easy :)!!! Now comes the question: My 
top-left corner should be (0,0) and my lower-right corner (xmax,ymax). 
How can I do this in a pspicture environment? Everything that I tried 
(xunit, origin, swapaxes, etc) always give lower-left corner (0,0). 
Below is some example.

Pedro

\documentclass{minimal}
\usepackage{pstricks,bm}
\usepackage[papersize={643px,482px}]{geometry}
\geometry{margin={0pt,0pt},centering,ignoreall,dvips}
\pagestyle{empty}
\usepackage{helvet}
\renewcommand{\rmdefault}{phv}
\begin{document}
\noindent
\begin{pspicture}(0,482pt)(643pt,0)
\psframe[fillstyle=solid,fillcolor={[HTML]{E4F2FF}},linestyle=none](0,0)(643pt,482pt)
\rput[t](321pt,460pt){\psscalebox{3.0}{{\color[HTML]{0200F0}$\bm{%
\mathrm{X}_3}$ \textbf{pseudo-rotation}}}}
\rput[rb](-635pt,-7pt){\psscalebox{0.8}{\mbox{\gray%
\usefont{OT1}{phv}{b}{n}\copyright\ Varandas \& Caridade (2006)}}}
\end{pspicture}
\end{document}