[kh99]

You should look in admincp/usergroup.php, and look for

($hook = vBulletinHook::fetch_hook('admin_usergroup_edit')) ? eval($hook) : false;

around line 201. That's where your hook code is executed. You can see that the admincp code uses a set of functions to print out html for the forms, so you can use one of those functions yourself is you want. I think if you name your input tag "usergroup[something]" and create a db column in the usergroup table named "something", you might not have to do anything other than print out the html for your form field. Otherwise, you would need code (probably in a plugin on hook admin_usergroup_save) to handle your input field when the form is submitted.