language files

I’m setting up WordPress for someone in Dutch. Since WP 2.5 was giving me problems I wanted to use WP 2.3.3 but the Dutch version is no longer available for download. So I downloaded the dutch .mo, .po and wordpess.pot files. I know I have to put the .mo file in the wp-includes/language folder but where do I put the .po and wordpess.pot files?

The codex doesn’t include that info in the articles on translating WP