[XML]
<?xml version="1.0" encoding="EUC-JP"?>
<a>
<b name="A県">
<c name="A市"/>
<c name="B市"/>
</b>
<b name="B県">
<c name="C市"/>
<c name="sapporo"/>
</b>
</a>

[XSLT]
<?xml version="1.0" encoding="EUC-JP"?>

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="EUC-JP"/>

<xsl:template match="a">
<result>
<xsl:apply-templates select="b"/>
</result>
</xsl:template>

<xsl:template match="b">
<xsl:apply-templates select="c[@name='sapporo']"/>
</xsl:template>

<xsl:template match="c">
<xsl:value-of select="count(../preceding-sibling::b) + 1"/>
</xsl:template>

</xsl:stylesheet>

[結果]
<?xml version="1.0" encoding="EUC-JP"?>
<result>2</result>