document.onkeydown = NavigateThrough;

function myKeyDownHandler(){
  alert("A key down event took place within the document!");
}

function NavigateThrough (event)
{
	switch (event.keyCode ? event.keyCode : event.which ? event.which : null)
	{
		case 0x25:
			link = document.getElementById ('PrevLink');
			break;
		case 0x27:
			link = document.getElementById ('NextLink');
			break;
		case 0x26:
			link = document.getElementById ('UpLink');
			break;
		case 0x28:
			link = document.getElementById ('DownLink');
			break;

	}
	if (link && link.href) document.location = link.href;	
}