You're not making yourself very clear. What exactly is your problem?
Your example looks fishy because the test asks about an attribute @Tooltip, while the body looks at a child element Tooltip. It seems unlikely that you have both.
What makes you use this verbose xsl:element/xsl:attribute notation, when you could write
<asp:label id="{ttip_@name}" runat="server" text="{@Tooltip}"/>
Are you paid by the line, perhaps?
Michael Kay
http://www.saxonica.com/
Author, XSLT 2.0 and XPath 2.0 Programmer's Reference