HowTo: Make a field part of the registration process
To make a field part of the registration, perform the following steps:
- Go to: Administer >> User management >> Profiles.
- Create the profile field if it doesn't exist yet, and as follows:
- Under the 'add new field' section, choose the type of field you want to create by clicking its link.
- Provide the particulars for the field, namely category, title, form name, explanation, weight, visibility and page title.
- Now check whether the field may or may not be left empty.
- To make it appear on the registration page, make a checkmark in the 'Visible in user registration' checkbox.
- Click on the 'Save field' button.
Your new field will now appear on the registration page.
Note that in Drupal 4.6 and 4.7 the links are found in administer >> settings >> profiles.
Visibility Notes
I've found some stuff by trial and error. These are not bugs, just observations :-)
This is valid for 4.7 where New Members Applications are blocked pending Admin Approval.
1) Hidden fields do NOT show in Registration, even if made mandatory and flagged to appear in Registration.
2) Private fields will show, but only AFTER the initial Username / Email request, at which point they pop up (in angry red if they are required fields).
3) Public appear as you'd expect - up there on the Registration page.

mandatory fields
When I mark a list as mandatory drupal fills in the first value in the list. So the field is not empty but the user could register without fillining in any info and just register with the default value.
Otherwise the field has no default value when the field is marked as "can be empty".
How can I make a mandatory field with no preselection?
I would like to know this too.
I would like to know this too.