var dm=new Object();
	dm.minTop=0;
	dm.maxTop=20;
	dm.inc=1;
	dm.time=new Array();
	dm.objs=new Array("about","products","clients","contacts");
	dm.moveAll=function(par)
	{	for(var i=this.objs.length-1;i>=0;i--)
			if(obj(this.objs[i]).offsetTop!=this.maxTop) this.buttonMove(this.objs[i],0);
		this.buttonMove(par,1);
	}
	dm.buttonMove=function(par,dir)
	{	if(this.time[par]) clearInterval(this.time[par]);
		var ob=obj(par);
		if(dir||ob.offsetTop)	ob.inc=-this.inc;
		else 					ob.inc=this.inc;
		if(!dir) ob.inc=this.inc;
		this.time[par]=setInterval("move('"+par+"')",18);
	}
	
function move(id)
{	var ob=obj(id);
	if(ob.offsetTop<dm.minTop)
	{	clearInterval(dm.time[id]);
		ob.style.top=dm.minTop;
	}
	else if(ob.offsetTop>dm.maxTop)
	{	clearInterval(dm.time[id]);
		ob.style.top=dm.maxTop;
	}
	else ob.style.top=ob.offsetTop+ob.inc;
}