[pstricks] Why pspicture environment does not work in plain TeX

[VAFA KHALIGHI]

This is a minimal example

\input pstricks
\begin{pspicture}(0,0)(2,2)
\psline(0,0)(1,1)
\end{pspicture}

\end

TeX does not recognises pspicture environment, I am using MiKTeX2.7 with
latest updates. If the answer is that pspicture is not to be used in Plain
TeX, then is there anyway that pstricks figures do not overlap the texts?
Thanks heaps
-- 
"I hope to die ___ _____
before I *have* to use Microsoft Word.", 0--,| /OOOOOOO\
Donald E. Knuth, 02-Oct-2001 in Tuebingen. <_/ / /OOOOOOOOOOO\
\ \/OOOOOOOOOOOOOOO\
\ OOOOOOOOOOOOOOOOO|//
Vafa Khalighi \/\/\/\/\/\/\/\/\/
// / \\ \
^^^^^ ^^^^^
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