I'm a programmer, I have an idea, I know how to implement it, it will be a website, and that site will be my business.

My question is very basic: where in timeline must I register my business as an official Company (ie, according Government laws)?

Here there are some options to debate or to help answer me:

1. Now - or as soon as I have the idea;
2. When looking for investors (e.g., when a prototype or business plan is ready);
3. When implementing the website;
4. At site's launch;
5. I must launch the website as a personal informal business and, when the business gets success and turns into a more solid and self-running one, only then I must formalize it;
6. It doesn't matter; I can create the company when I want.

Nobody talks about that. If I just have an idea, must I run into an office to create a Company? I don't think so. When I'll look for investors, the Company must to pre-exist? Or will the Company be formed with the investor?

I'm looking for a generic, country-independent answer, but may the answer for your country can be useful to me. I'm Brazilian, and I believe that the country doesn't matter to this question.

(Sorry if this is off-topic, but I coudn't find a batter stackexchange site to ask this.)