You can pretend the node represents XML document or XML fragment you
want to validate, then nothing special should be done. The only problem
is then in .NET 1.0 and 1.1 one cannot validate XmlDocument in-memory,
you have to get XML as text and then read it via XmlValidatingReader.
Something like

XmlTextReader r = new XmlTextReader(new StringReader(node.OuterXml));
XmlValidatingReader vr = new XmlValidatingReader(r);
vr.ValidationType = ValidationType.Schema;
while (vr.Read());