Spinach Pesto and Spaghetti

1 pound whole wheat spaghetti
1 10-ounce package frozen spinach, thawed, well-drained
2 Tablespoons olive oil
1/4 (one-quarter) cup grated Parmesan cheese
2 tablespoons chopped fresh parsley
2 cloves garlic
1/2 (one-half) teaspoon salt
1/2 (one-half) teaspoon dried basil
2 tablespoons butter
1/3 cup warm water
4 ounces crumbled Feta cheese

Prepare pasta according to package directions. Drain, rinse and keep warm. In blender or food processor, combine spinach, oil, Parmesan cheese, parsley, garlic, salt and basil. Blend at medium speed or process until finely chopped. Melt butter in water. With blender or processor running, gradually pour in melted margarine mixture until blended. Toss with pasta. Sprinkle Feta on top and serve eight.