Not really sure where you are going with this but will offer up some reading material as a starting point.

There is a CPAN Module Net::YahooMessenger that should get you started with the bulk of the work, which seems to be interfacing with Yahoo.

For the database stuff, obviously you are going to want to bone up on DBI

For a tutorial on DBI, you should check out this thread which appears to have many examples and suggestions regarding the path to enlightenment.

There is also working with files and databases from tutorials.

Lastly, I offer up the obligatory "check out merlyns columns"...there you will find a hoard of examples that are sure to result in an epiphany.