[C0M0Y0K0]

What the easiest way to reset this computer, so that when turned on it has no data on it and goes through the configuration screens?

[Leonard]

Restart the machine from the system CD/DVD by inserting the disc into the machine and restarting holding down the "c" key. Once it starts up, select disk utility from the menu and reformat the HD (this will erase all data on the machine). Once that is done, quit disk utility and the MacOS X installer will take over again. Follow the steps to install MacOS X and the iapps.

[Sherman Homan]

I would only add that the erase option has a couple of choices, simply erasing does not really get rid of the data. Your files and folders will still be there, they will be hard to find and potentially overwritten by the reinstallation process. But if you choose "zero all data" you will actually rewrite a stream of zeros over your files making them much harder to recover. Then depending on your level of paranoia you can take several zero all data passes.