9
Sorry, my #2 suggestion above applies to changing things in the "Edit Profile" form.
To edit the "Register Now" form, go to include/registerform.php and change the text box settings for the fields you want to change. The first number is the text box width you want to change, the second number is the maximum text length allowed for that field - which should be the same as that field setting in its MySQL table.
For example, to change the email box width, at approx line 40 in include/registerform.php:
$email_text = new XoopsFormText("", "email", 25, 60, $email);
change the number 25 to whatever you want (leave the 60 alone!) and that's the new width (in pixels.)