Be warned! This can be dangerous as it deletes also userdata!
!denrad eB
Be warned! Do not remove root, or you'll lock out yourself!
!denrad eB
For SuSE it's possible: Open up Yast and go to users and groups, you can delete users there. Or you can use the console and issue an "userdel <user>" ("man userdel" first! Danger of loss of data!).
What is windows?