Dynamically Update ListBox Item

I have as a ListBox item a reference to a ScrollingLine class, in which I
override ToString() to return the part of text currently visible in a
scrolling window. How do I get my ListBox to update its display of that
string? Does it make a copy of the ToString() result of each item when
initialising, or does it just not know to update and maybe I could
invalidate it?

Take a look at this:
http:// blogs.korzh.com/progtips/2008/03/15/update_listbox_item_in_windows_forms.html

Please remove all space at that URL (sorry I can not place the links as new user).