function ol_open(url, params)
{
	$('overlay_content').innerHTML = 'loading ... ';
	$('overlay').className = 'show';
	var vp_width = document.viewport.getWidth();
	var vp_height = document.viewport.getHeight();
	var vp_scroll_offset = document.viewport.getScrollOffsets();
	var top = vp_scroll_offset.top+((vp_height-150)/3);
	var left = (vp_width - 420) / 2;
	$('overlay').setStyle({top: top+"px", left: left+"px"});
	new Ajax.Updater('overlay_content', url, { parameters: params, method: 'post' })
}

function ol_open_tall(url, params)
{
	var height = 400;
	$('overlay_content').innerHTML = 'loading ... ';
	$('overlay').className = 'show';
	var vp_width = document.viewport.getWidth();
	var vp_height = document.viewport.getHeight();
	var vp_scroll_offset = document.viewport.getScrollOffsets();
	var top = vp_scroll_offset.top+((vp_height-400)/3);
	var left = (vp_width - 420) / 2;
	$('overlay').setStyle({top: top+"px", left: left+"px", height:  height+"px"});
	new Ajax.Updater('overlay_content', url, { parameters: params, method: 'post' })
}


function ol_close()
{
	$('overlay').className = 'hide';
}