If you have an ATI graphics card, update it. That is supposed to help, although from what I heard it doesnt.
What worked best for me is to turn the camera around and have your character run towards the screen. It takes a little bit of effort to get exactly to where you need to - just try to follow the map. Also, try to stick to the edges the best you can. Moving into the middle of the fields tends to bring the lag back, even when running towards the screen. It's certainly not a fix but it made the Datoinne part playable for me.
I never tried the vertex buffer fix - sounds promising.