creating many-many relation

I'm trying to create a many-many relation between computers and
programs.

I've got the DB set up correctly (id in each table and a
computers_programs table with computer_id and program_id). Ideally,
I'd like to have on my computesr/edit page a checkbox for each program
that, when updated, creates the record in the computers_programs table.

I've no clue how to go about doing this.

Could someone possibly boil this down into an outline so I can get a
better idea of what I have to figure out?

Thanx!