How to jump to top of browser page

You can set the scrollTop, like this:

$('html,body').scrollTop(0);

Or if you want a little animation instead of a snap to the top:

$('html, body').animate({ scrollTop: 0 }, 'fast');

Without animation, you can use plain JS:

scroll(0,0)

With animation, check Nick's answer.

If you're using jQuery UI dialog, you could just style the modal to appear with the position fixed in the window so it doesn't pop-up out of view, negating the need to scroll. Otherwise,

var scrollTop = function() {
    window.scrollTo(0, 0);
};

should do the trick.

You could do it without javascript and simply use anchor tags? Then it would be accessible to those js free.

although as you are using modals, I assume you don't care about being js free. ;)