Help I'm stuck with this XSLT malarky.

I've got data something like below (made up names to keep it simple?!)
I want to create a HTML document with a table for everything with group 
0 and another table for the rest. Within each table I'd have a different 
looking row depending on if it's a Car or a Bike.

I've managed to get it to sort all the groups an output a header for the 
first group 0, but I can't work out how to work out when I've got the 
last group 0 and the first/last non group 0.

It would be possible to have no items in either group.

Help!!

Thanks,

<xsl:for-each select=" //Group">
<xsl:sort select="." data-type="number"/>
	<xsl:if test="../Group=0 and position()=1">
		Ungrouped Vehicles
	</xsl:if>

	<h1>Group:</h1>
	<xsl:value-of Select="../Group"/><br></br>
		...
		...
</xsl:for-each>


<Contract>
	<Client Detail>
	....
	</CLient Details>
	<Cars>
		<Car>
			...
			<Group>1<Group>
		</Car>
	<Cars>

	<Bikes>
		<Bike>
			...
			<Group>2<Group>
		</Bike>
		<Bike>
			...
			<Group>0<Group>
		</Bike>
	<Bikes>
</Contract>