Hi,
mostly lurk here but thought i'd add my suggestion for training as I am an avid skier. In addition to an exercise regimen that involves many of the types of exercise discussed above, I have found that the most beneficial training method for improving my overall performance on the slopes is core training and balance training. No matter what level you ski at, you will be surprised how much working on core strength and balance will help you. As we all know, a strong core will help you keep proper posture and alignment that is necessary for efficient, safe, and correct skiing (i'd suggest cathe's CoreMax dvd for a good training program, pilates also). Also, for balance training, performing various strength training exercises (especially lower body) on an unstable surface will help you develop greater strength, flexibility, and control while on your skis. For example, doing squats while one foot is on a plastic balance disk, or doing upper body work on a balance ball (gets core too). A good cardio cross training option is to roller blade. Roller blading, especially in the off season, keeps not only your heart conditioned, but your legs conditioned for the skating motion necessary to power over flat terrain when on your skis. Finally, be sure to incorporate regular stretching. Women are prone to knee injuries when skiing, so keep your muscles flexible will help to prevent problems. I usually warm up before hitting the slopes or take a few easy green runs to start the day to warm up. Hope this adds to the great advice you've already been given. Love the summer but can't wait till winter!
Catie