You can add href= and text = by using WriteAttributeString
..
Try the below code.. May be it will help you...
writer.WriteStartElement("itunes:image")
writer.WriteAttributeString("href", "http://www.mywebsitehere.com/student.jpg")
writer.WriteEndElement()
writer.WriteStartElement("itunes:category")
writer.WriteAttributeString("text", "Education")
writer.WriteStartElement("itunes:category", Nothing)
writer.WriteAttributeString("text", "Education Technology")
writer.WriteEndElement()
writer.WriteEndElement()
writer.WriteStartElement("itunes:category")
writer.WriteAttributeString("text", "Education Technology")
writer.WriteEndElement()