All I really need on my joomla site is one more blank on the user registration form to ask how the user was referred to the site.

I was told to check out CB.

My site has SMF integrated into it and coppermine intgrated into smf.

Will CB 1.0 break my site?

Can anyone tell me how to simply edit a php page (which one) so that I have the extra field I need?

CB may be overkill.