access a form from other forms

Question

Hi,
I have two forms. there is a listBox in form1 and I need to add to this listBox from FORM2.
It is not too hard, but I may need to add an item to another form's listBox.
I mean maybe I will have a third form witch contains a listBox and I must add the item form FORM2 into that listBox.
I hope I could explain curefully.
Please Help
Thanks