Recently we had to take over some old Drupal 5 sites and bring them into our Aegir hosting platform. We had a few problems getting it all running smoothly so though we'd detail the steps involved.
- copy your doc root files to platforms/yoursite
- make sure no path specific guff in .htaccess (shared hosting note suPHP_config_path)
- chown all of the files to aegir:apache/aegir:www-data depending on whether it's a Debian or Red Hat based distro
- create your database and import your database dump
- run a database prefix stripper if needed and edit setting.php accordingly
- edit profile.info, node.info, drupal.info, comments.info and enclose the description in double quotes
- edit clear.inc in your drush install and add if function_exist('node_types_rebuild') before the call to node_types_rebuild
- if you've got any modules from drupal.org - be sure to remove the 'information added from drupal.org packaging script on' (there's a bash script floating around to do this)
- change drush.inc to handle non-array returns for $info (line 665)
- change your sites/default to something meaningful so the platform verify picks it up
- create your platform in aegir
- if it all runs to plan your platform will verify and your site will be imported
- run the verify task on the imported site
- migrate your site to the latest drupal 5 build using aegir
Obviously the next step from here is to convince the client to upgrade it to Drupal 7 or at the very least Drupal 6.