If your project is auto scheduled then you can add task constraints for each task using the ConstraintType and ConstraintDate properties. First you specify which type of constraint for the ConstraintType property. The ConstraintType property provides the following type of constraints:

Constraint Type	Description
Default	No constraint.
StartNoEarlierThan	Specifies the earliest start date for the task. Use this constraint to make sure the task does not start before a specified date. This constraint is selected by default if the task is a successor.
StartNoLaterThan	Specifies the latest start date for the task. Use this constraint to make sure the task does not start after a specified date. This constraint is selected by default if the task is a predecessor.
FinishNoEarlierThan	Specifies the earliest finish date for the task. Use this constraint to make sure the task does not finish before a certain date.
FinishNoLaterThan	Specifies the latest finish date for the task. Use this constraint to make sure the task does not finish after a certain date.
MustStartOn	Specifies the date the task must begin.
MustFinishOn	Specifies the date the task must end.

Once you have selected a constraint type for the task you can specify the constraint date using the ConstraintDate property.