Posts navigation not working

Like the topic says, I’m having trouble with the post navigation links. I’ve tried using posts_nav_link() at the bottom of my page and some of the other link functions in template-functions-post.php, but everything returns blank. The div tags I have around the navigation links show up just fine, naturally, but there is nothing inside.
I’ve set posts_per_page to match the total number of posts so they’ll all be readable, but this is not something I’m prepared to live with ?? Is there a simple solution I’ve missed?
I’m running the 2004-02-20 nightly, and besides this one thing everything is running smoothly.