SUDDEN RUDDER

I was on final at DFW airport Runway 36L, winds were calm, headed 177 at 8kts. I was flying the POSKY 757-200 Delta NCC. Lined up with the runway, I opened flaps to 30 degrees, slowed to 140kts, and deployed the gear. All was going nicely. I had to make a few adjustments to line up perfectly, however, when it looked like I was perfect with the runway, the ADF would tell me I wasnt exactly on course, so I ignored it. The glideslope would soon indicated that I was slipping off to another direction, so I would correct a little bit, and then the same thing would happen over and over again. About 500 ft AGL, the GPWS gave it's announcement. I crosschecked all of the instruments, and made my final correction. I then noticed I forgot to take off ATT, so I switched it off, feeling confident. The aircraft mainted 140 kts, lined up, descending at 500 fpm. Then, all of a sudden, about 100ft AGL, the aircraft started to yaw to the left, as if I had suddenly put full rudder into it. I quickly opened rudder in the oppsite direction, but I was too late, the aircraft touched on the runway, and rolled off before I could keep it on course. Ticked off, I shut off the sim and ignored taxiing to the gate. As I look back, I try to figure out the problem. On my departure from Portland Oregon, I had a slight crosswind, so I did use a little bit of rudder, but after departure, I turned into the wind, and so I centered it, and the autopilot would have done it anyways, as it flew the course. I figure it can't be an error with the aircraft, since it comes from such an important manufacturer. Any ideas, what could have gone wrong. Could it be anything besides the rudder? On my particular panel, I dont have a rudder indicator.