How do I get that "Comment Posted!" effect as seen on YouTube?

Hi.

I guess my description was too long and got cut short. I'm referring to this: http://s4.tinypic.com/awq2pu.jpg

I was looking at the source code for the buttons before and after posting, but couldn't figure it out. I'd like to be able to scroll through the message, too, like you see here: http://s4.tinypic.com/27yy7ms.jpg

Does anybody know how?

Much thanks.