Hi Ice,
You've got some nice shots, but they're not altogether sharp unfortunately. The second one is unacceptably out of focus, while the other two lack critical focus as well. When you're just starting out, stick to safe shots with a faster shutter speeds. You've achieved a significant amount of panning effect, which can be reduced. A slightly higher shutter speed will help on the sharpness front, of the main subject of course.
I'd stick to the 100-300 and forget the 28-200. Try to get access to more inside corners if you can, these usually pack more impact with the rider leaning in towards you, as in the third shot. Watch your exposure, I don't know if it's the scanning or the printing or the exposing, but somewhere along the way you're losing highlight detail. The blank white patches on the first two shots are unacceptable, and are both a bit overexposed/overprinted anyway.
Otherwise you're doing well. Shoot lots, that will get you more experience and give you more opportunity to capture vital moments -- wheelies, crashes, etc. Being more comfortable with the camera to your eyes will help you get more familiar and help you react better as well.
Good luck! :thumbsup: