Rockstar:

window.scrollBy(0,0);

First 0 is your x, or width, scroll, second 0 is your y, or height, scroll, in characters or rows. This will actually scroll.

window.scroll(0,0);

This does the same thing, only it jumps to that part of the page instead of scrolling, so the animated effect of scrolling does not occur.

Scroll by a button:

function scrollDown(){
window.scroll(0,10);
}

function scrollStop(){
clearInterval(scolling);
}

In the button, set an interval and a clear:

<input type="button" value="v" onmousedown="var scrolling=window.setInterval(‘scrollDown()’, 50);" onmouseup="scrollStop();" />