I have a list box with user names recorded in it..what i'd like to know is how
to write a function so that if a user name dissapears from the list box then
flash takes a specific action, such as printing "a user has left the room" in a
seperate dynamic text box .

will you please tell me how that can be accomplished?

The user names are added to the list box dynamically via a php script.

The user name is put to a flash variable via a php script then the user name
variable is place inside an RSO object then the user name is put to a list box
if a user logs off or closes his browswer window then the RSO object is updated
and the list box is updated.