>the _screen.objects(nindex)... allows to uniquely identify an object in the _scree but how can i know this 'nindex' for a form ? Is there a command which returns this number ? i'd like to get it in the init event of the form.

If you want it in the Init(), its probably the largest number, but I wouldn't rely on it. What are you giong to do with it? You should build your own Forms Manager.