Put the value in a variable and use it repeatedly withing the for-each loop:
<xsl:template match="Order"><xsl:text/>
<xsl:variable name="ref" select="normalize-space(./OrderReferences)"/><xsl:text/>
<xsl:for-each select="./OrderLine">
<xsl:value-of select="$ref"/>
<xsl:value-of select="normalize-space(LineNumber)"/><xsl:text/>
<xsl:value-of select="normalize-space(Product)"/><xsl:text/>
<xsl:value-of select="normalize-space(Quantity)"/>#013;<xsl:text/>
</xsl:for-each>
</xsl:template>
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference