San Francisco International (SFO) and Oakland International (OAK) are both about an hour from Petaluma.
All of the major car rental agencies are at either airport. There are Airporter shuttle services (Airport Express and Santa Rosa Airporter) hourly from both airports that will bring you to Petaluma, Rohnert Park, and Santa Rosa. The trip currently costs about $18/person one-way, and $30/person round-trip. Be sure to ask for the senior or student discount if you qualify. When you board the bus, ask them to call whoever is going to pick you up in Sonoma County.
There is an airport in Sonoma County (STS). United flies shuttles from SFO and LAX on most days. Prices vary, depending on if you are adding on to an existing United flight or not.
The Wedding is in Petaluma, the southernmost town in beautiful Sonoma County. This area is renowned for its wine and fun activities.
We've made a group block at the Good Nite Inn in Rohnert Park. They are located 20 minutes north of the Brewer Ranch. They've given us very good rates.
The rates are for June 4, 5, and 6, 1999 and are per room - Number of people depends on you. Reservations must be made by May 14, use confirmation number 18452. Dogs are allowed. You can even make reservations online through their website or call 1-800-Nite-Inn (648-3466).
If you are looking for something a little more upscale or closer to Petaluma, there are dozens of places. Check out some of these sites:
Sonoma County Convention & Visitors Bureau - they'll send you a free guide, too