The XML Team posted on March 3, 2007 a more detailed description of the LINQ to XML bridge classes to System.Xml. This post includes simple C#-only (of course) code samples for XPath, XSLT, and XSD validation.
The team's February 2, 2007 XML Features in the February CTP of Visual Studio “Orcas” post described the Bridge Classes as follows:
These implementations of System.Xml interfaces such as XmlReader, XmlWriter, and XPathNavigator will allow XPath / XSLT to be used over LINQ to XML trees, allow XSLT transformations to produce an LINQ to XML tree, and allow efficient data interchange between DOM and LINQ to XML applications. There is also a Validate extension method to validate an XElement tree against an XML Schema.
The new post explains the objective of the bridge classes more concisely:
[T]he whole point of the bridge classes [is] to mix-n-match LINQ to XML objects (which we hope are easier to use than XmlDocument objects, and can easily integrate with other LINQ providers) with existing code.
Again, it would be nice to see some VB 9.0 samples from the XML team.