If you want to migrate PHP Nuke to Joomla 1.5.15,this is the tutorials:

Howto:

1. Install fresh (do not install sample data) Joomla! 1.5.15.
2. Change cfg.php with your nuke site database variables.
3. put 2 files to joomla main directory (where configuration.php is)
4. run phpnuke2jos.php to your web browser (for example website.com/joomla/phpnuke2jos.php)
5. 2 options asked you "Migrate Users" and "Migrate Contents".