Errori su pacchetto pstricks

Buongiorno a tutti,
sto provando a muovere i primi passi con pstricks ma ho un errore fin dal primo banale esempio trovato in una delle tante presentazioni presenti sul web:
Presentazione
Ora, il codice che inserisco è questo:

`
\documentclass{article}
\usepackage{pstricks}

\begin{document}
\begin{figure}
\begin{pspicture}(4,5)
\psframe(0.7,2)(3.3,3)
\rput(2,2.5){First Example}
\end{pspicture}
\end{figure}
\end{document}
`

ma quando compilo mi da errori come “la presenza di un doppio documentclass o documentstyle che proprio non comprendo…
Premetto che mi succede sia su ambiente windows sia linux.
Gli errori sono i seguenti:

`
This is pdfTeXk, Version 3.141592-1.40.3 (Web2C 7.5.6) (format=pdflatex 2008.9.22) 11 FEB 2009 20:19
entering extended mode
%&-line parsing enabled.
**piripicchio.tex
(./piripicchio.tex
LaTeX2e <2005/12/01>
Babel and hyphenation patterns for english, usenglishmax, dumylang, noh
yphenation, loaded.
(/usr/share/texmf-texlive/tex/latex/base/article.cls
Document Class: article 2005/09/16 v1.4f Standard LaTeX document class
(/usr/share/texmf-texlive/tex/latex/base/size10.clo
File: size10.clo 2005/09/16 v1.4f Standard LaTeX file (size option)
)
\c@part=\count79
\c@section=\count80
\c@subsection=\count81
\c@subsubsection=\count82
\c@paragraph=\count83
\c@subparagraph=\count84
\c@figure=\count85
\c@table=\count86
\abovecaptionskip=\skip41
\belowcaptionskip=\skip42
\bibindent=\dimen102
)
(/usr/share/texmf-texlive/tex/latex/pstricks/pstricks.sty
Package: pstricks 2006/08/10 v0.32 LaTeX wrapper for `PSTricks' (RN,HV)
(./pstricks.tex

! LaTeX Error: Two \documentclass or \documentstyle commands.

See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
…

l.1 \documentclass{
article}
The document may only declare one class.

(./piripicchio.aux)
\openout1 = `piripicchio.aux'.

LaTeX Font Info: Checking defaults for OML/cmm/m/it on input line 4.
LaTeX Font Info: … okay on input line 4.
LaTeX Font Info: Checking defaults for T1/cmr/m/n on input line 4.
LaTeX Font Info: … okay on input line 4.
LaTeX Font Info: Checking defaults for OT1/cmr/m/n on input line 4.
LaTeX Font Info: … okay on input line 4.
LaTeX Font Info: Checking defaults for OMS/cmsy/m/n on input line 4.
LaTeX Font Info: … okay on input line 4.
LaTeX Font Info: Checking defaults for OMX/cmex/m/n on input line 4.
LaTeX Font Info: … okay on input line 4.
LaTeX Font Info: Checking defaults for U/cmr/m/n on input line 4.
LaTeX Font Info: … okay on input line 4.

! LaTeX Error: Environment pspicture undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
…

l.6 \begin{pspicture}
(4,5)
Your command was ignored.
Type I to replace it with another command,
or to continue without it.

! Undefined control sequence.
l.7 \psframe
(0.7,2)(3.3,3)
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

! Undefined control sequence.
l.8 \rput
(2,2.5){First Example}
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

! LaTeX Error: \begin{figure} on input line 5 ended by \end{pspicture}.
[SNIP………]
`