var cumulativeOffset = function(element) {
var top = 0, left = 0;
do {
top += element.offsetTop || 0;
left += element.offsetLeft || 0;
element = element.offsetParent;
} while(element);
return {
top: top,
left: left
};
};
(Method shamelessly stolen from PrototypeJS; code style, variable names and return value changed to protect the innocent)