migration

I'm working on a fairly large migration project. For this project, I will be migrating legacy data into Drupal 6. For this, I would like to create a new node with a specified nid so I can import data and maintain correct paths. I have looked everywhere for any tips on how to accomplish this, however, it doesn't seem like a very common practice. I have considered adding aliases, but for my case, I really feel like if I can directly map legacy ids to drupal nids, it will really make my life easier down the road. Has anybody had success doing anything like this?