Best, lightweight and multiple-browser-compatible way to do fancy Javascript dialog boxes (pop-up window replacement)

Hello,

I'd like to implement (at first), two separate things:

- a 'button' that would always be available at a fixed place (even for pages spanning multiple screens) that would call the second thing:
- a 'window' (in fact a superimposed <div>) that would contain two or three text entries and a form. Ideally, this 'window' should be resizable and movable.

I can more or less see how to program it by myself, but if I do so, I believe that I'll have cross-browser problems and that it will be a 'reinventing the wheel' kind of exercise.

I know there are JS libraries (that is why I ask this question in the Jquery subsection also) for doing this kind of things. Are they the best answer to my simple needs? Or does simple 20-lines, rather optimized code to do so, exist?

What matters the most to me is that the library (or snippet of code) is non-bloated, easy to understand and implement (if it is a library, it needs a good documentation), quick to load and, before all, work on all browsers, from IE 5.5 to the latest incarnations of Firefox, Safari and Opera.

If it works well, I'll probably write a complete (although modest) web application using these 'widgets', so it is OK and even desirable that the solution can do a little more than what I asked.

Thanks,
Stéphane