Thanks Ramana,
Here's where I'm stuck. The IP 2007 example uses the
XPathNavigator xn = this.MainDataSource.CreateNavigator();
to get the xpath navigator object. To my knowledge this object is not available in the IP 2003 managed code solution. I'm guessing there's a workable convesrsion from the form's secondary datasource xml to an xpath comaptable format so the navigator can be created, but I'm not sure what that conversion is. I'm pretty sure it involves a namespace manager object but I can't seem to get it working.
Thanks!