Migrating users:
To migrate users from PHP Nuke to Drupal takes two simple MySQL commands. The following examples are for going from PHP Nuke 5 to Drupal 3.

First, you need to be sure that the 'name' column in the PHP Nuke user table isn't blank. For example, from within MySQL type:update phpnuke.nuke_users set name=uname where name='';

Second, copy the valid data from the PHP Nuke user table to the Drupal user table:insert into drupal.users(name,userid,real_email,fake_email,url,bio) select name,uname,email,femail,url,bio from phpnuke.nuke_users;

If you find this intimidating, you can try this script which includes more instructions.