Não é uma solução sed mas uma XSLT
<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
<xsl:output method="text" />
<xsl:template match="//table/tr">
<xsl:value-of select="descendant::td[1]"/>
<xsl:text> </xsl:text>
<xsl:value-of select="descendant::td[2]"/>
<xsl:text> </xsl:text>
<xsl:value-of select="descendant::td[3]"/>
<xsl:text> </xsl:text>
<xsl:value-of select="descendant::td[4]"/>
</xsl:template>
</xsl:stylesheet>