Change of status to immigrant visa from VWP....possible?

Hi, I am a British national with a US fiance. I have been working as a journalist on an I visa, and recently lost my passport and visa. I am planning to marry my fiance in February in the US, and then apply for the immigrant visa, green card.

I am wondering whether I need to get a new I visa to enter into the US in February, or if I enter through the Visa Waiver Program (tourist visa), will I then be able to change my status to an immigrant visa once in the US?

The embassy website seems to suggest not, but so many people get their change of staus even when they have been living illegally in the US and then get married, it makes me think that it doesn't matter what you entered with, as long as you are not in violation of status when you apply...ie. within the three months. It makes me think that it doesn't even matter if you are in legal status in the US...marriage seems to wipe the slate clean....but I want to make sure before I apply.

Thanks for replying -