/wp-content/plugins/theme-my-login/templates/register-form.php

<form>

<p>
	<label for="first_name<?php $template->the_instance(); ?>"><?php _e( 'First name', 'theme-my-login' ) ?></label>
	<input type="text" name="first_name" id="first_name<?php $template->the_instance(); ?>" class="input" value="<?php $template->the_posted_value( 'first_name' ); ?>" size="20" tabindex="20" />
</p>
<p>
	<label for="last_name<?php $template->the_instance(); ?>"><?php _e( 'Last name', 'theme-my-login' ) ?></label>
	<input type="text" name="last_name" id="last_name<?php $template->the_instance(); ?>" class="input" value="<?php $template->the_posted_value( 'last_name' ); ?>" size="20" tabindex="20" />
</p>