property LineStyle: LongWord;

LineStyle can be one of these XlLineStyle constants.

xlContinuous

xlDash

xlDashDot

xlDashDotDot

xlDot

xlDouble

xlSlantDashDot

xlLineStyleNone

This example puts a border around the A1:C5 range.

Workbook.Sheets[1].Range['A1', 'C5'].Borders.LineStyle := xlDot;