DW,
They've changed their reservation procedures a bit recently, so I'm not sure of the latest tips (you can prob find them someplace like chowhound), but in the past I've had success two ways:
1) call in the morning and check opentable right when the reservation lines open and cross your fingers.
2) if that doesn't work, check every night after that for cancellations on the days you're interested in. Any cancellations used to pop up on open table at the same time every night (like 10p or midnight iirc).
Meadowood is the other wine country 3-star Michelin, and reservations are much easier. Big debate amongst foodie types out here about which of the two is better; lots of people say Meadowood.
http://www.therestaurantatmeadowood.com