To select a node that's in a namespace, you need to use a prefix. Any prefix will do so long as it's bound to the right namespace. E.g.
<xsl:apply-templates select="x:xform" xmlns:x="http://www.w3.org/2000/xforms"/>
You would normally declare this namespace on the xsl:stylesheet element because you will probably be using it all over the place. Note that the children of the xform element are also in this namespace.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference