Hi Jeff,
You should be able to apply a paragraph border, this assumes that your paragraph is not set to be only 2.5" wide.
Border setting are applied using the Borders and Shading dialog. You can access it from the Paragraph group on the Home tab of the Ribbon; it's under the last button on the bottom row right. Look down the menu for Borders and Shading.
You want to be on the Borders tab of the dialog, have the Apply To box set to Paragraph, and select a Style of Line that you want. Then click it the preview box for where you want the border line to appear... top or bottom. If you make a mistake just click
the line again and it is removed.
If you want this border line to extend into the margins... then look into Stefan's suggestion about left and right indents.
Kind Regards, Rich ... http://greatcirclelearning.com