yup - mod\choice\mod.html
approx line 109
$standardblanks = 10;
Increase this number to the amount you need!
Sorry if I sound very new now but where would I find that?
in your moodle install, - find the file, Mod\choice\mod.html then make the change mentioned above.
Just discovered in Moodle 1.8 a button "Add 3 fields to form" which enables you to add another 3 choices and another 3 and another 3...
look for the value:
$repeatno = 5;
in the file mod_form.php
Increase it to the number that you would like!