Thanks Joe,

this is what I ended up with.
Its not pretty because it really doesn't examine the primary key part of the 
schema definition properly. But it does a ok job.

<?xml version="1.0" encoding="utf-8"?> 
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:od="urn:schemas-microsoft-com:officedata">
<xsl:output method="xml" indent="yes" />
<xsl:template match="node()|@*">
	<xsl:copy>
		<xsl:apply-templates select="@*|node()" />
	</xsl:copy>
</xsl:template> 
<xsl:template match="*[@minOccurs=1 and @od:jetType='decimal' and 
position()=1] ">
		<xsl:comment> Changing decimal to autonumber </xsl:comment>
		<xsl:copy>
			<xsl:apply-templates select="@name|@od:sqlSType|@od:nonNullable" />
				<xsl:attribute name="minOccurs">1</xsl:attribute>
				<xsl:attribute name="od:jetType">autonumber</xsl:attribute>
				<xsl:attribute name="od:autoUnique">yes</xsl:attribute>
			<xsl:apply-templates select="node()" />
		</xsl:copy>
</xsl:template> 
</xsl:stylesheet>