I'm not real clear from what you've said whether it'll be helpful or not, but you can set up INT()-typed primary key fields to be auto-incrmenting. You can leave the field out of your INSERT statement, or insert NULL into the field, and the database will automatically give you the next number in that field.
Code:
CREATE TABLE Demonstration (
rownumber INT(5) NOT NULL PRIMARY KEY AUTO_INCREMENT,
modelnumber VARCHAR(255),
type VARCHAR(255)
);
(I am renowned far and wide for my properly capitalized SQL statements.)