This website has extensive information about what an IEP is, how it runs, and what to do if you have a problem. The only thing I would add to their list of things to do when an IEP goes wrong is to call an attorney. The website has a lot of resources about special education. It also give a you a list of agencys and people to contact if you would like more information (#16 Information Resources)
This page is from the California Department of Education which can supply you with information specific to California as well as general special education information. This page goes over the basic rights promised to a parent of a special education student and a short explanation of what that means. There is also contact information at the bottom if you would like further information.
The place where special education lawyers and professionals go to research special education law. The website is dense and some of the language is technical but if you have a question about special education law the answer will likely be on the site.