Hi,
I improved it in this way:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0" xmlns:msxsl="urn:schemas-microsoft-com:xslt">
<xsl:output method="html"/>
<xsl:key name="RouterList" match="Router" use="Supplier"/>
<!-- Template for our root rule -->
<xsl:template match="RouterList">
<xsl:for-each
select="//Router[generate-id(.)=generate-id(key('RouterList',Supplier))]">
		<xsl:sort select="Supplier" order="ascending"/>
		<xsl:variable name="ok_op" select="Supplier" />
    	<div style="background-color:#f2f2f2;"><img border="1"
src="http://www.miosito.com/images/logos/{(Supplier)}.gif"></img><br></br>(<xsl:value-of
select="$ok_op"/>)</div>
      <xsl:value-of
select="//Router[Supplier=$ok_op]/GroupList/Group/OutwardList/Outward/Price/Amount/text()"/>

		<br/><br/>
	</xsl:for-each>
</xsl:template>
</xsl:stylesheet>

In this way:

 <xsl:value-of
select="//Router[Supplier=$ok_op]/GroupList/Group/OutwardList/Outward/Price/Amount/text()"/>

I found the Price/Amount relative for each supplier But I didnt found
the min value ofr the supplier.....

I need some advice...
Thanks a lot.