Harry Potter uses the Class as Defense Variant rule, which can be found on the SRD. Wizards/Witch's use the column B Defense table.
Vitality and Wound Points
Harry Potter d20 uses Vitality and Wound Points as found here in the SRD if the GM wishes.
http://www.d20srd.org/srd/variant/adventuring/vitalityAndWoundPoints.htm