Horizontal Bar Which 'sticks' To The Window?

I was wondering if it was possible to have a horizontal bar on a page that 'sticks' to the page. For example a bar which always sticks to the top or bottom and doesn't move despite the window scrolling up and down.

My first idea was to get the windows scroll and offset the horizontal bars position based on that, however Javascript doesn't seem to get updated very often on the scroll and it produces a nasty snap and pull effect.

One way around that effect is to have the bar glide into place like this demo does: [URL]

But I really don't like that.

I actually didn't think doing this was possible until I saw the Google Friend Connect script here: [URL]

As you can see there's a horizontal bar at the bottom which doesn't suffer from any drag latency and 'sticks' to the window.

I was wondering how i could duplicate that effect, or am I just aiming too high and google knows something no one else does?

It looks like they're using frames but I don't understand, wouldn't that mean that the main frame will be the horizontal bar frame and if so shouldn't that mean the head link should be pointing to the frames location instead? :S