If you are running a windows server, you'll need the nwnx_funcs plugin for
NWNX2. It has a boot-PC-with-message script function.
This references the default dialog.tlk file, so your players will need a customized version of that file for it to function correctly. It won't read a custom .tlk file in the NWN/tlk folder.
I do this for my PW (for CD key checks, server resets, etc.). It works pretty slick, but players won't see the right message without that altered dialog.tlk.