Pages: How to put a word between horizontal rules
With Pages it helps to think in terms of layers.  Combinations of Text Boxes and Line graphics layered and arranged, should achieve the desired result.  Determine beforehand if the graphic and text box should cause wrapping and/or move with the rest of the text in the document or remain static.
Create a Horizontal Rule with Text Centered

Add a Line graphic to the canvas (Just one line will do)



Position the line horizontally to the desired width
Set the Object Placement properties in the Arrange tab on the Inspector as desired.



Add a Text Box setting the Text style Alignment properties to Center and Middle



IMPORTANT: Change the background color from None to a color matching your document's background.  (White typically)
Set the Object Placement properties as desired
Position the text box over the line.  Use the alignment guides to center on the page


By using layers, one can create many interesting effects.  Some of them can be explored by examining the built in templates.