Right, you're going to want to have duplicates for model id, Furthermore you're inserting into a field that's intended for auto increment so you will likely get unexpected results.
focus (mfg 6)
explorer (mfg 6)
So you will need another auto increment field for the purpose of a unique id. something like
CREATE TABLE `model` (
`id` int(11) primary key auto_increment,
`model_id` tinyint(4) NOT NULL,
`manufacturer_id` tinyint(4) default NULL,
`model_name` varchar(30) default NULL,
) TYPE=MyISAM AUTO_INCREMENT=1;
This will allow you to keep tinyint for model_id and also allow duplicate values for that field, which is likely what you want.