I'm developing a small website to use with my N800, and have trouble showing
a small popup window (not fullscreen).

Now the question is, has anyone ever seen a small popup window on N800?
Is the N800 even capable of resizing the browser window?

Windows are fullscreen only.

Nah, I've seen one pop up that was smaller, and it killed my browser for a while.

what do u mean "killed" your browser? it stopped working completely?

@rezigrene -- never seen a non-fullscreen popup on microb before. Could you send me the URL that gave you this? Even the pop-ups at my bank's web site display in the full window on microb, and smaller windows on my desktop

prove it, or i call troll

You mean like this?
http://spacecoastvelosport.com/home.html

I did it with dhtml.

You can't do a separate browser window that's not full-size.
Javascript windows are possible, if you just need to notify/query the user.
For more complex stuff, you can play with divs, spans, etc. with css.
Check http://meyerweb.com/eric/css/edge/ for some examples.

I can't remember the URL. I was just surfing around, and got a pop-up for an OMG FREE LAPTOOP. If I remember correctly, and I am, it was definitely smaller that my full browser, but had a box-frame on it (as if you were clicking the window to see the contents under it). It was very odd, but I could still exit the browser and bring it back up. I probably should have noted what did it.