Hello there!! I have a question that is killing my brain...

I had asked for a change of status in august/2007 to B-2 visa and I didn't receive any response yet (according with the processing time they are working on June applications). Is it possible to change a visa only with the receipt number??? Cause I want to change to F-1 Visa... Even if I'm waiting for the response am I illegal in the country? Or can I stay until 6 months after I've filled my application? Can I ask for the visa after receiving my new visa status, even if it's expired? How long can I wait until I have to come back to my country and ask again (there) for a new Visa?

Well... as you can see, I'm really confused... Need help, please!!
Thanks!