If you tried all of the suggestions in that topic, then the only thing left, that I can think of, is to:
1) remove mIRC using Add/Remove Programs (or whatever it's called in Vista)
2) remove any and all files that may be left (not necessarily delete, just make sure they don't exist in the installation directory).
3) download a fresh copy of the mIRC installer from here
4) Run the installer for a Full install (if it shows an upgrade installation as default, change it to the Full install).