Preheat the oven to 350 degrees F (175 degrees C).
In a medium bowl, mix together the margarine and cream cheese until well blended. Beat in flour, 1 cup at a time, until the mixture forms a smooth dough. Roll into small balls, and press into the bottoms and sides of tart pans or mini muffin pans.
In another bowl, mix together the eggs, brown sugar, butter, vanilla, and salt. Stir in the pecans. Use a spoon to fill each of the crusts 2/3 full with the filling mixture.
Bake for 15 to 18 minutes in the preheated oven, until shell is light brown, and the filling has puffed up. Cool, and carefully remove from pans.