Use the mouse to select any line (not a cursor point inserted into a line in a position ha), open the format - border and background - border, you can see the right side of the preview box has the upper and lower left and right four delineation buttons, click to select the upper or lower horizontal line knob, click on OK to exit to see the effect, how ah, you want to separate the line is not a done deal.
2003 version I remember I can also find the right-click to expand the menu on the border and background, 2007 version of the same.
2010 version can use the shortcut alt + 06
2012 version is not finished, I guess it is the same as 2010 version.
Slowly finish ha, I go also.