Hi Nils,
If you wanna chk whether the tag is empty (as in this case <tag></tag> ) or whether the tag is not there at all ... you can use a generic thing which will do both of it ... Assuming that the tag is <name>, you can use the xsl given below to do this,
<xsl:if test="count(name/text()) != 0">
Hope this helps...
Vicks.