70-200 f/2.8 will be ideal I'd imagine for this sort of thing. hopefully you'll be able to get close enough to the action to get some really good shots.
As far as advice goes, just the usual good panning techniques and (using S priority) a slower shutter speed to give a sense of high speed. follow the line of the car into the bend, click, and follow it out again, as smooth as possible, you'll soon pick it up.
If there are other people there on the day, why not try and practice on them first so you don't miss the important shots
move around the stage/circuit as much as possible to get the best vantage point, as low as you can get to the ground also works well.
on the outside of bends (if they will even let you stand there), a faster shutter speed (your f/2.8 should be perfect for this) and closeups through the windscreen for the grin on the face of your other half, and the face of horror from the instructor
With your camera and lens you should have no problem with cropping-in tighter on the computer afterwards if you need to, but a Low ISO will help keep the quality if you think you need to do this, depending on how the light/weather is. and RAW is the way forward for this type of thing, you'll probably want to tweak some Exposure/WB afterwards. (i'm probably teaching my grandmother to suck eggs, arn't I?). anyway..
Good luck, Dav! please post your results here and you can get some good c+c from people far more experienced than me.
