<p>In Visual Studio you can create a template XML document from an existing schema. The new <a href="http://msdn.microsoft.com/en-us/library/cc716766.aspx" rel="noreferrer">XML Schema Explorer</a> in VS2008 SP1 takes this a stage further and can create a sample XML document complete with data.
Is there a class library in .NET to do this automatically without having to use Visual Studio? I found the <a href="http://msdn.microsoft.com/en-us/library/aa302296.aspx" rel="noreferrer">XmlSampleGenerator</a>  article on MSDN but it was written in 2004 so maybe there is something already included in .NET to do this now?</p>

Directly, none that I can think of, other than third party add-ons. You could utilize the
xsd schema definition tool
to take your XSD and create a .NET object/class, once you have that, you could, to quote the linked page:
XSD to Classes: Generates runtime classes from an XSD schema file. The generated classes can be used in conjunction with
System.Xml.Serialization.XmlSerializer
to read and write XML code that follows the schema.