If I understand you correctly, you want to pass the selected
id (or something) to a popup window, correct? If so:
In your detailWin class, you can define a property of the
correct type (if id is an int then define a property of type int.).
This property should be "public" and writeable. So let's call this
property "selectedId" for discussion sake.
Once you have a reference to you popup window:
var detail :Object =
mx.managers.PopUpManager.createPopUp(this, detailWin, true,
simply set the property in that instance:
detailWin.selectedId = [the id from your grid';