August Grand Prize: a 2011 Chevy Corvette and a check for $15,800. (ARV: $78,950)
September Grand Prize: A custom road trip package including a $7,500 Gift of Travel certificate, a check for $3,500, a Garmin Nuvi, luggage, a 4-room tent, a camera, and more. (ARV: $12,881.61)
If (and only if) you receive a Marlboro Country Rewards promotional mailing, you can call the toll-free number to enter by telephone.
Note that there's another promotion going, where you can explore the Marlboro site to get points toward rewards. But you don't need to explore the site to enter the sweepstakes.