Email upon comments

hello all,I have a question...
what code do i need that i can put in certain pages that send a email to users if there profile (or other pages of theres) has been commented on?
follow me?
if a member has there profile commented on,what is the code i need to put in so that member receives an email stating they have a private message waiting at my site?
not just comments in profiles but other places like member pages from venue.
what code do i need to put in each page that will send a email,not just a PM to members who have certain pages commented on?
hope ya get what i mean?
where would i put this send email code on each of the pages i'd like to add it to?

any help appreciated!