In Delphi you can access the individual borders of a table cell (i.e. top, bottom, left, right, vertical, horizontal, diagonal down and diagonal up) using the Borders property of an individual cell.
e.g.
OleVariant(MyWordDocument.Tables.Item(0).Cell(0,0)).Borders(wdBorderTop)
As you can see from my example, I have found that I need to typecast the Cell as an OleVariant to access the borders property, but I haven't yet figured out why. You can then check the properties of the border, such as Visible and LineStyle.
The best place to find out the properties and methods of objects in Word is in the help file of the Visual Basic Editor in Word.
Steve