What would cause front end vibration in a 02 Sable - Taurus that starts at about 45mph?

Answer 1

Have all the wheels checked for balance.

NOTE: wheels can be balanced on a typical stand-alone machine, but for the most comprehensive approach, they can balance on the car.

Something to consider

If the wheels are fine, then something else is wrong - and the best thing to do is have the front-end inspected by a professional. Ask for referrals at your local auto parts store(s) to a top-notch front-end specialty shop.