As Suzanne suggests, if the line is to be level with the centre of the text height then it is a bit fiddly to achieve manually, but you can do it with a macro.
Type the heading text at the left margin then run the following macro, which sets tabs at the centre and right margins with underline leaders, then tabs are added before and after the text and formatted raised to the height ot the font divided by 2.5, which
should be near enough the centre. You can adjust that figure to whatever you need to produce the effect you are after
Sub AddLines()
Dim iWidth As Long, iLM As Long, iRM As Long, iCentre As Long
Dim oHT As Long
Dim oRng As Range
With Selection.Sections(1).PageSetup
iLM = .LeftMargin
iRM = .RightMargin
iWidth = .PageWidth
End With
'find the cenre of the page between the margins
iCentre = ((iWidth - (iLM + iRM)) / 2)
'Clear any existing tabs and add a tab at the centre and another at the right margin
With Selection.ParagraphFormat.TabStops
.ClearAll
.Add Position:=iCentre, _
Alignment:=wdAlignTabCenter, _
Leader:=wdTabLeaderLines
.Add Position:=iWidth - iLM - iRM, _
Alignment:=wdAlignTabRight, _
Leader:=wdTabLeaderLines
End With
'define the paragraph text as a range
Set oRng = Selection.Paragraphs(1).Range
oRng.End = oRng.End - 1
'establish the font size of the first character
oHT = oRng.Characters(1).Font.Size
'add a tab before and a space and tab after the text
oRng.InsertBefore vbTab
oRng.InsertAfter Chr(32) & vbTab
'move the range start and end to include the tabs
oRng.Start = oRng.Start - 1
oRng.End = oRng.Paragraphs(1).Range.End
'locate and format the tabs by raising the font
With oRng.Find
Do While .Execute(FindText:=Chr(9))
oRng.Font.Position = oHT / 2.5
Loop
End With
'collapse the range
oRng.Collapse wdCollapseEnd
'and select it to continue typing from that point
oRng.Select
End Sub
http://www.gmayor.com/installing_macro.htm