I don't really understand what your problem is :
Here are two ways to do it.
1) Assuming namespace is hardcoded in your xslt.
<xsl:template match="/"><rss xmlns:tv="http://www.rss-tv.org/rss/tv1.0" version="2.0"></rss></xsl:template>
2) Assuming you get the namespace from some other parameter :
<xsl:template match="/"><xsl:variable name="namespace">http://www.rss-tv.org/rss/tv1.0</xsl:variable><rss xmlns:tv="{$namespace}"/></xsl:template>
Create an element with your desired result.