True acclimatization to a higher altitude only happens after a few months. The best thing you can do to prepare yourself is interval training or cardio that builds up your wind and lowers your resting heart rate.
Lots of swimming or long distance running.
Last time I had a general checkup my doctor thought something was wrong with me due to my low resting heart rate. I run several half marathons a year and am typically at the gym 9 times a week. I wasn't joking about being a fitness rat.
I've been to Peru (11,000 ft) and only suffered from slight headaches in morning for the first few days. The water however gave me super colon blow.
You will probably still end up taking the START Bus in. Jackson is a ski where you really do not really need a car. The (extremely) rich folks who run things in Jackson do what they can to discourage skiers from driving in everyday to ride the mountain. There is a pay-to-park lot close to the base of the mountain, but there is a free-to-park satellite lot just a few miles down the road.
All of the START Buses on their way into the village and on their way back into town stop there. If you already have a car, I would drive to the lot, park there and just deal with the 7 minute, free bus ride to the resort.
Bring a book or magazine for the ride home. Don't forget to take a picture of the 3rd largest potato in the world in Driggs :-)
Thanks for the pointers.