The Bay Area is one of the best spots on the globe for sailing sports and there are many spots to learn to sail, either on a dinghy or on a wind surfboard.
Required equipment: generally none. The same place that has the boats will generally have the PFDs, and spray gear. Note that some places may strong urge, if not require the use of a wetsuit so you may want to have your own. Hats, sunglasses, and as always, sunscreen, may be helpful.
Required time commitment: one weekend. Classes are typically two 4 hour sessions, or perhaps two such weekends for sailing. After that, it's a typical half day activity.
Costs: Cal Adventures teaches sailing in two courses, 16 hours each. Each class costs roughly $200 (less if UCB affiliated, tad more if not). They also offer two 8 hours windsurfing classes at 80/100 each. Instruction is done in the Berkeley Marina. I've taken both of these courses - they cover all you need to know to become a decent small boat sailor and have a bit of racing practice as well. Sailboats and wind boards rent at $15/hr or $150 per 2 month pass. A $50/yr membership reduces these fees down to 12/120.
At Foster City, California Windsurfing offers a 2 day (6 hour) intro for $95. This was my introduction and I found it to give me the basics to learn this variant of sailing. The Foster City lagoon is very calm which can be helpful as you learn to balance on a board. Sometimes, however, the wind is too light, particularly before the afternoon. Graduates of the course receive a preferred card which lets them rent all day for $20, a great value.
The Cal Sailing Club is a cooperative that may be a good choice for someone that wants to learn both, and lives in the area. Membership is $50/quarter or $150 for the year. For that, you can rent all you like, and get all the instruction you need for windsurfing, dinghies, and even larger keel boats. However, this is a coop - the lessons are given by members when they are available to do so. Each active member is expected to contribute at least 2 hours of service per quarter in instruction or maintenence. I no longer live nearby, so I did not find out myself how well it works.
Cal Sailing Club
California Windsurfing - Foster City.
Bay Area Wind Patterns