Again, I'm not sure exactly what you are doing but you could use an invisible sprite (chatpos) that acts as the locator for the new chat line and have it move to the new position at the end of the function.
You can pass parameters to the function to determine who's avatar and message will be shown
on message pending - call function 'chat' w parameters (username,chattext)
Function 'chat'
create object by name "avatar"&username at chatpos.imagepointX("username"), chatpos.imagepointY("username")
create object 'text' at chatpos.imagepointX("text"), chatpos.imagepointY("text")
text - Set text to "chattext"
chatpos - move at 90° text.heightpx+10px