(Not tested)
<xsl:function name="my:ajax-link">
  <xsl:param name="href" select="'x'"/>
  <xsl:param name="text" select="'y'"/>
  <a href="{$href}" onClick="showData('{$href}');return
false;"><xsl:value-of select="$text" /></a>

</xsl:function>

<value-of select="my:ajax-link($href, $text)"/>

I'm not very familiar with the ins and outs of 1.0 , but I don't know of
a less verbose way to call a named template in either version....