Mix sugar, sweetened condensed milk, coconut, and vanilla together. Form into long rolls about the diameter of a nickel. The mixture will be sticky, so use waxed paper in forming the rolls. Freeze until firm. When ready to dip, melt the chocolate chips in a double boiler. Cut the frozen rolls into 1-inch logs or 1/2-inch nuggets and place on a fork. Lower the candy into the chocolate mixture and coat the entire piece. Place on a cooling rack to harden. Variations: Vary the chocolate flavors by using semisweet chocolate chips or milk chocolate or mint-flavored chips. A nut half may be placed on the top of each log and dipped along with the candy. Finely chopped nuts or candied fruit may be added to the coconut mixture.