These days I was struggling with this problem: I needed to scroll the page (using javascript) to the embeded swf object. After some search and tests I used the following function (found here) to find the Y position of the object.
function findPosY(obj) {
var curtop = 0;
if(obj.offsetParent)
[...]
If you need to find the length of an object, and I mean the number of children of the specified object, use the following function/method:
public static function getLength(o:Object):uint
{
var len:uint = 0;
for (var item:* in o)
if (item != "mx_internal_uid")
[...]