Is there any easy way to restore a (leopard) system without the factory disk? If not, is it possible to manually go in and delete everything? If so, where would one find system preferences, key chain for pass codes, other sensitive information, etc?
EDIT: Oops! Thought of the free space thing after I left for awhile. I see that Weaselboy beat me to the punch. I use TechTool Pro for that, and wasn't sure that Disk Utility had that option. I'll take the Weasel's word for it.
Yes. Just delete the old user data when asked as you remove the account. Then go to your new account and start Disk Utility and do a secure erase of free space.