First of all, sorry for the late reply, guys. DX

@Haseo
Yup, that's what I was planning to do. But I was too shy to do it. lol! XD
As you mentioned it in your post that Gendou is insanely smart at things like this. While I know that, I realize that I'm a 100% n00b. XD

So, It will be kinda stupid if I ask him... and he answers... and then I could only reply it with...
"huh?" or "Ummm... I don't get it" or "Wh-What is that?"-kind of replies. XD
So I open up a thread instead... hahahahahahah XD

@Unico
Ah, Ajax... XD
My friend told me to use that too. And now I'm using it for my chat application. XD
Currently, I'm using a free AJAX-based chat from some sites, then I(and my friends) just simply modified them.
Well, time goes on and I(and my friends) have to finished it quickly, so there isn't much time to learn how to make a chat from scratch. lol! XD
(since our target was... kinda insane for a beginner. (like me and my friends XD)

By the way, thanks for the information, unico.
I really appreciate it! I'm taking a look now. XD

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Btw, I just find out that Gendou.com's chat always fits with any window size.
and it forces to use scroll when it goes really small.
But it seems only for vertical resizing, I found out the chat will be messed up when I resizing it horizontally (to a very small width).

I wonder what CSS code to make it 'always fit with any size'... XD
Like... when the size is below 500px, use scroll... instead of maintaining the page layout which will definitely be messed up when resizing it into a really small window.

I try utilizing the min-width and width code.
It works and then I manage to make my chat can handle any horizontal resizing.

then I used the min-height and height code for handling vertical resizing,
but somehow it doesn't work. XD

It's pretty funny to see that gendou.com's chat can only handle vertical resizing,
while I can do the opposite, that is can only handle horizontal resizing. XD

Anyone has an idea? o.o