ここがid="container"です

参考サイト - Archiva v2.2 | A note of notions. On web, tech, and myth.

JavaScript部分

/*

 scroll.js | v1
 --------------------------------------------
 Copyright 2007 Sig. - http://archiva.jp
 
 Licensed under the Creative Commons Attribution 2.1 Japan License
  - http://creativecommons.org/licenses/by/2.1/jp/

 Functions:
 --------------------------------------------
  - smScrollTop
  - smoothScroll
  - getElementPos
  - setScrollPosition

 Function Calls:
 --------------------------------------------
 xxxxx.onclick = function(){
 	smScrollTop();
 }
 
 xxxxx.onclick = function(){
 	smoothScroll(this,'obj_id');
 }

*/



/* ------------------------------------------ *
 * smScrollTop()
 *  - no require
/* ------------------------------------------ */


function smScrollTop(){
	var pos = new Object();
	pos.x = document.documentElement.scrollLeft || document.body.scrollLeft;
	pos.y = document.documentElement.scrollTop || document.body.scrollTop;
	
	window.scrollTo(Math.max(Math.floor(pos.x / 2),0), Math.max(Math.floor(pos.y -(pos.y / 5)),0));
    
    if (pos.x > 0 || pos.y > 0) {
        window.setTimeout("smScrollTop()", 10);
        return false;
    }
}


/* ------------------------------------------ *
 * smoothScroll(base,move)
 *  - require start object and ID of goal object
/* ------------------------------------------ */

var timer;
var distance = 0;

function smoothScroll(base,move){
	var base_pos = getElementPos(base);
	var move_obj = document.getElementById(move);
	var move_pos = getElementPos(move_obj);
	distance = move_pos.y - base_pos.y;

	var sdLength = 200; // 減速開始距離
	var sdRatio = 6;   // 減速率
	var speed = 120; // 移動速度

	timer = setInterval( function(){ setScrollPosition(sdLength,sdRatio,speed) },10);
}

function getElementPos(elem) {
	var obj = new Object();
	obj.x = elem.offsetLeft;
	obj.y = elem.offsetTop;

	while(elem.offsetParent) {
		elem = elem.offsetParent;
		obj.x += elem.offsetLeft;
		obj.y += elem.offsetTop;
	}
	return obj;
}

function setScrollPosition(sdLength,sdRatio,speed) {
	var moveValue = 0;
	
	if(Math.abs(distance)>sdLength){
		moveValue = (distance>0) ? speed : -speed;
	}
	
	else {
		moveValue = Math.round(distance/sdRatio);
	}
	
	parent.scrollBy(0,moveValue);
	distance = distance-moveValue;

	if(moveValue==0){
		clearInterval(timer);
		distance=0;
	}
}

body部分

<div id="container">ここがid="container"です</div>
：
ほにゃらら
：
<a href="#container" onclick="smScrollTop(); return false;" title="ページの先頭へ">ページの先頭へ</a>