i would like to write something like this :

<xsl:variable name="counter" select="0"/>
<xsl:for-each select="toto">
    <xsl:variable name="counter" select="$counter+1"/>
</xsl:for-each>

And about variables - that's a very very very faq, so check out XSL FAQ:
http://www.dpawson.co.uk/xsl/sect2/N8090.html
--
Oleg Tkachenko
Multiconn Technologies, Israel