Hi there! I live in your neck of the woods. (Closer than my city name suggests. ;) My husband and I own a business, so although I'm technically employed full-time, I have a lot of help and can delegate freely at work. I also work from home most of the time, so that's helpful.
Anyhow, a great resource is www.hsc.org. They have a conference every summer (usually at the Red Lion near Arden Fair, but this year it will be in Santa Clara).
There are many local homeschooling co-ops. Some are more involved and structured than others. If you are religious, there are more options to choose from, and in some of these co-ops, parents will teach a certain subject in exchange for another parent teaching another subject (I'll teach French, and you can teach Biology, or whatever). We belong to a co-op mostly for park days, crafts, the occasional science day, and the like. (Sacramento Fun Homeschoolers - check it out on Facebook and MeetUp).
You should definitely check out A Brighter Child in Citrus Heights. They host classes in all kinds of subjects for homeschoolers, and have curriculum available, as well as lots of supplementary items. It's like a teacher store, but for homeschoolers.
If you don't want to go through a public charter (like CAVA K12, Visions in Education, or Horizon Charter), then you just have to register with the state of California as a private school. It's very easy to do (HSC can point you in the right direction). As to whether you can legally homeschool other people's children (or they yours), people do it all the time in a co-op setting.
For what it's worth, we are currently switching from K12 to Oak Meadow, and from public school charter to private/independent homeschooling. If you're new to homeschooling, K12 isn't a bad option to look into. It is very structured, and is a complete curriculum ("curriculum in a box," as it's called in the homeschooling world). The only reason I'm switching away from it is that my youngest is a very kinetic learner, and I felt like Waldorf would be a better fit for her. I have several friends in the area who use everything from Sonlight to Abeka to Natomas Charter to Horizon Charter to K12. If I can answer any questions, let me know!
For what it's worth (since some of the moms here "worry for the homeschooled child"), homeschooled children are FAR above the national average in terms of test scores. Last I checked, the average homeschooled child scored in the 87th percentile across the board (vs. the 50th percentile for the average public school student). No need to worry for us, we're doing just fine! http://www.washingtontimes.com/news/2009/aug/30/home-scho...