Proposing legislation

[renaissanceguy]

I live in Illinois, which is predominantly a "blue" state that is rather progressive about gay rights. Right now we have a non-discrimination bill pending in our state legislature (alongside a blanket anti-gay-marriage measure which is not likely to pass).

I would like to propose to the legislature a bill that would provide civil unions or gay marriage. But I don't quite know how to go about it. How does one start a petition? What happens after people sign on to the petition?

I've obviously never done this before, but I feel that Illinois stands a really good chance to getting this passed. Any suggestions or ideas?