Bring water to a boil in a medium saucepan; add shrimp, and cook 3 to 5 minutes or until shrimp turn pink. Drain well. Set aside, and keep warm. Melt margarine in a saucepan over medium heat. Add garlic; saute 1 minute. Stir in flour. Gradually add milk, stirring with a wire whisk until blended; cook, stirring constantly, 8 minutes or until thickened and bubbly. Stir in cream cheese, cook 2 minutes. Add 1 cup cheese, stirring constantly until it melts. Pour over fettuccine; toss well to coat. Add shrimp; toss gently. Top with remaining 1/4 cup Parmesan cheese, parsley, and pepper.