Sprinkle fillets with tarragon, pepper, and salt. Bring 4 cups water to a boil in a large nonstick skillet over medium heat. Reduce heat, and add fillets; cover, and simmer 8 to 10 minutes or until fish flakes easily when tested with a fork. Remove fish from liquid, and place on a serving platter; discard liquid. Set fish aside, and keep warm.
Heat olive oil in a nonstick skillet over medium-high heat until hot. Add garlic; saute 1 minute or until tender. Add Madeira; cook 1 minute or until reduced to 2 tablespoons. Stir in lemon juice and capers; cook until thoroughly heated. Pour sauce over fish, and sprinkle with parsley.