I am trying to make a form scroll down the page as the user scrolls. See here:
http://bit.ly/9qIcSq

It seems to work fine just by setting:

#sidebar form {
    width: 190px;
    padding: 12px;
    background: url('../image/sidebar-form.png') no-repeat;
    margin-left: 15px;
    overflow: hidden;
    position: fixed;
    top: 145px;
}

But when it gets to the bottom of the page it overlaps the footer. Is there any way using CSS that I can get it to stop above the footer when it gets to that point?

Or would I need to use JavaScript?

Thanks.

Is there any way using CSS

Nope. Though you could give the "footer" a higher z-index to make it go "underneath"

Or would I need to use JavaScript?

Yep.

JavaScript it is then