how to make a log in pop-up at the top corner of the forum

[Ravenstar]

hi,
ive seen on another forum, a button that says "Login" on it, and when you click on it , a small pop up comes up, with the "log in attributes" .....

here are some screen shots to help:

this is when i click on it:


can anyone tell me how to get this,
or do i need the CSS/widget/JS code for it...