the only way to find out the ids relating to pictures, strings etc is to look through the ui files. It can sometimes be a long process to find the right one, but it's the only way. The best place to start however, is the 'Extraction Log' created by Plus! when you extract messenger's resources(with consolidated files turned on). This lists the window numbers and what they relate to, for example:
quote:
Originally posted by Extraction Log.txt
Consolidating Windows Files:
Window 919: success! (browser)
Window 920: success! (convframe)
Window 921: success! (main)
Window 922: success!
Window 923: success! (mainwnd)
so if you want to edit the mainwnd, you know you're looking for any file that ends in 923.(e.g msgres_4004_923 would be the definition file for it.)
Willz is also releasing a 4th part to his skinning guide which will detail all the different resources and what they do.
Other than just guessing/trial and error there isn't any other way of finding what the id is you're looking for.