The Derby? The best race you'll ever enter. Not to mention the fact that if you are into crazy fall you die descents, La Grave has plenty of super-scary stuff and unless you regularly ski there, you should get a guide. You'll need a harness and rope and know how to rescue yourself from crevasses as well as rappel into and out of chutes.
For the Derby, get your legs nice and strong and get a really good tune/wax job. the start is a long flat gliding section, and then it's 6000 vertical feet to the bottom down steep rocky lines, through trees, bumps, etc to the finish. You need the wax for the first section and the strong legs to get you to the finish.
have fun, it's one of the best parties in Europe.