Difficulty importing user table from another drupal installation

I have two drupal installations, a live version and a dev version. I'd like to copy only the user table from one to another, is this possible? I've tried exporting the users table sql, and importing again, everything runs ok until a new user tries to register, they're being assigned a uid field that's been taken by my new import of users. Where's this uid number coming from, can anyone help?

I've also tried editing my exported user sql, replacing all the imported ids with 0 (it's a regular mysql database and the uid is auto increment), but still having the same issue when a new user tries to register:

user warning: Duplicate entry '58' for key 1 query: INSERT INTO users (name, mail, pass, init, status, created, uid) VALUES ('foo', 'foo@clarkeology.com', 'f1cb12dac984f0bcffb330185aecdd13', 'foo@clarkeology.com', 1, 1168595643, 58) in /data/www/dev.maliceboxquest.penguin.inside.poke/public/includes/database.mysql.inc on line 121.

Thanks