My Abbey gets carsick too.
We have done so much with her, before she couldn't even be in the car 10 minutes without throwing up--now I can get her to my parents' (2 hours)

We give her dramamine or an anti-anxiety remedy. I got something from our local pet store that I just put on a treat and feed it to her--it helps calm her down.
The short rides helped her out a lot too, especially taking her to places she loves!!!

I don't think she'll ever be much of a rider, but I try to make her as comfortable as possible when she *has* to be in the car.