How does one create a pop up window where the pop up is not a Web browser

Hi,

How does one create a Pop Up window where the window that pops up is not
a Web browser via the Javascript Open command but the window that opens
up is a custom window but it is still HTML.

To see what I mean for example go to:

and click on the Log-in link that is on the top right corner. Once you do then a small window pops up where you can enter your userrname & password. This is the type of a pop up window that I need to create.

Also please do not suggest JQuery as the solution, but the actual Javascript and other code.

Regards,

They are more commonly known as modal windows, here are 2 searchs i made.

Native JS
jQuery

Well 1st Thanx for letting me know what they are called.
Since it is/was such a pain to try to describe them.
Now that I know what they are called I am going to search for it
and i am sure I will find the related code quick.

ThanX again.