Problems with <xsl:param name Help!

[kirashet]

Hello everybody,

I tried to make a XSL:FO - Sheet where I can control if the PDF should
be printed in portrait or landscape.
My results so far:

<xslaram name="printingtype" select="'landscape'">
<xsl:variable name="pageheight">
<xsl:choose>
<xsl:when
test="$printingtype='landscape'">21</xsl:when>
<xsltherwise>29.7</xsltherwise>
</xsl:choose>
</xsl:variable>
<xsl:variable name="pagewidth">
<xsl:choose>
<xsl:when
test="$printingtype='landscape'">29.7</xsl:when>
<xsltherwise>21</xsltherwise>
</xsl:choose>
</xsl:variable>

It works, but not in that way I want ^^
And now my question: How can I control the | select="'landscape'" |
value... I tried everything, but I must say that I'm not long familiar
with XSL...

A nice hint would be very nice

greets