I forgot to install Pathauto on one of my sites. After downloading and installing it I was STILL left with my old /node/123 links all over. I assume that Pathauto only creates the aliases for new content but man would that be a pain. There had to be a pay to get it to generate aliases for old content.
Here is how I found it:
Step 1. Google
Step 2. BAM!
Step 3. Follow instructions over at: http://drupal.org/node/236304