. . but the major parties are pretty firm on wanting closed primaries so it's not going to change any time soon.
California in 1998 passed a completely open primary initiative that allowed you to vote a mix of candidates and was immediately sued by both major political parties. A U.S. Judge and the subsequent appeals court upheld the California law, but the U.S. Supreme Court (yes, the same one that appointed W President) said that violated "free association" and forced the political parties to "associate" with persons with philosophies they did not agree with.
California has a [link|http://reforminstitute.org/cgi-data/issues/files/14.shtml|rewritten initiative] in the works now for a second try.