Creating a Rakefile

A couple questions concerning rakefiles?

1) Where should I store Rakefile within my rails project? Within the
task folder? (if not then what is task folder meant for?)
2) How do I extend the pre-existing rake tasks? For instance if I
want to create a "rake db:populate_db" task
3) Is active record and the models within my rails project available
to the rake task by default? If not how do I include them?

Thanks for your help :-).

Thanks for your help.

Your Friend,

John