Registration options - add a new checkbox

[Joe Blow]

Hi all,

I want to add a new checkbox option on the registration page, next to where it gives people the option of recieving messages from administrators and other members.

I know I have to modify the registration template... what else do I need to do and how do I go about doing this.

Any help would be appreciated.

Cheers!
Joe

Specifically what I want to do is add a prechecked checkbox that authorises me to send them promotional emails.

Then, from the email section of the admincp I want to be able to send specific emails to users that had this box checked?

Any ideas?