Enter the batting lineup as you normally would. Then switch your view to the other team's scoresheet. From there select View | Inning Totals. Make sure the horizontal scroll bar is all the way to the left. This is where you enter the pitchers. If a player in the batting order is already the pitcher, (s)he will show up here. If no pitcher is entered in the lineup, here is where you'd enter the non-hitting pitcher. This is also where you make pitching substitutions (whether you are using a DH or not).