go to a good hardware store, that sells metal. get a 60" piece of 1" wide flat aluminum.this is long enough to go across most windshields of cars. have 2 people, one on each side, hold aluminum stock and find the lowest point of the windshield curve and put it up agaisnt that should be the center.now on each corner get a measurement of how much window is exposed above the aluminum.this will give you number of how much to make the arc on the computer. in corel make a straight line the width of the windshield. find center, and now make a straight line, convert to object, then extrude, and drop the center of the line the same distance you measured on each corner of the windshield.
WALA!!!!