Since Boomer posted some code, I think I should too..
To add IP's to customer registration, customer changing profile, and adding to newsletter from profile do following.
Code:
db_query("update $sql_tbl[customers] set password='$crypted', password_hint='$password_hint', password_hint_answer='$password_hint_answer', title='$title', firstname='$firstname', lastname='$lastname', company='$company', b_address='$b_address', b_city='$b_city', b_state='$b_state', b_country='$b_country', b_zipcode='$b_zipcode', s_address='$s_address', s_city='$s_city', s_state='$s_state', s_country='$s_country', s_zipcode='$s_zipcode', phone='$phone', email='$email', fax='$fax', url='$url', card_name='$card_name', card_type='$card_type', card_number='".text_crypt($card_number)."', card_expire='$card_expire', card_cvv2='$card_cvv2', pending_membership='$pending_membership', ssn='$ssn', ip='$_SERVER[REMOTE_ADDR]' where login='$login' and usertype='$login_type'");
Code:
db_query("insert into $sql_tbl[customers] (login,usertype,membership,password,password_hint,password_hint_answer,title,firstname,lastname,company,b_address,b_city,b_state,b_country,b_zipcode,s_address,s_city,s_state,s_country,s_zipcode,phone,email,fax,url,card_name,card_type,card_number,card_expire,card_cvv2,first_login,status,referer,pending_membership,ssn,ip) values ('$uname','$usertype','$membership','$crypted','$password_hint','$password_hint_answer','$title','$firstname','$lastname','$company','$b_address','$b_city','$b_state','$b_country','$b_zipcode','$s_address','$s_city','$s_state','$s_country','$s_zipcode','$phone','$email','$fax','$url','$card_name','$card_type','".text_crypt($card_number)."','$card_expire','$card_cvv2','".time()."','Y','$RefererCookie','$pending_membership','$ssn','$_SERVER[REMOTE_ADDR]')");
For displaying IP in customer profile, you can add following in MAIN/REGISTER.TPL