You should be fine just making changes to lib/MT/App/CMS.pm, yes; that contains all of the application code for the MT application itself. The subroutine you want is called "save_entry"; that is called whenever an entry needs to be saved (either creating a new entry or saving an existing entry).

Hello all,
I'd like to integrate MT with an existing message board. The "integration" consists basically in that when (and only when) an author makes a blog entry, some changes are made in a database (i.e. a forum is created).
The whole point is that I want to manage the blog part with MT but the "comments" with my old message board.

I've made a few changes to the code without success, should I look only to CMS.pm? Have anybody tried this before?.

thanks,
vega