[xsl] How to create a link with the value of node-set

[Ana Gaspar Martínez <annagaspar@xxxxxxxxx>]

Hello,
I wish to generate an url  from the value of one atrribute of the xml 
file. I've to transform this value to parse from the .xml to .html. I 
attemp that using the follow sentences:
<xsl:variable name= link>
<xsl:value-of select="concat(substring-first(var1,'.'),'.html')"/>
where var1=fichero.xml
</xsl:variable>
<a href="<xsl:value-of select="link"/> link1 </a>

But the xslt validator says that this is not valid...:( how can i do that??