For all I know (not a lot), it looks like the system is requesting a specific cookie before you can access that tax information.
How to acquire the cookie? Maybe by progressing through a certain sequence of web pages from the main Solano County web page. Do you remember how you got to the pages to which you linked?
Via RGSpinach's original links, in the Bush Protesting Mom Calls for 'Israel Out of Palestine' thread.