I have the same exact ford taurus 1999, and had this problem...
I've only had it two years, and I've had to fix A LOT on it... so don't be surprised if you have to as well.
I got my power steering pump replaced, and shortly after that I had to get my rack/pinion replaced as well (Which happened to be horribly expensive). I've had to drain out the steering fluid a few times for it to stop with the whining and jerking of the wheel, but I still can hear that whining once in a while. And also, I've had to get the ball joints replaced, the front right hub, and 2 pins in back replaced for support. I know I've had to get more fixed on it, but either way... It's probably going to end up that you'll be putting A LOT of money into this car...
Hope everything works out better for you!
Also, My car actually just broke down on me two days ago, and I've ruled out 3 different ideas of what's wrong. Tauruses are definitely not the best kind of car... =\
