how to add required 'Title' field to user registration

Hi, to u all :)
I'm a newbie fixing/upgrading a small web site that has implemented miniBB.
I need to change the user registration form so it contains a custom field, ' Title' with a combo box with Mr,Miss,etc. This field is required for registration and shouldn't be left blank.
Can anyone explain me how to do this ?
Tnx

Download Gender add-on and see how the dropdown box could be implemented.

Here is how to make profile's field mandatory.

Tnx Paul, I will try that