Just hose it down!
Kidding!! Kidding!! Please don't do that.
No original software?? Then you'll have to do a whole lot of deleting. And this won't really make the system the way it was when you bought it. You sure you don't have a software restore??
To re-install the system with no applications (the person you are selling this to can d/l them, right?), first erase the harddrive and then reinstall the system software. This will get you very close to how you got the computer in the first place (Just missing iMovie and maybe a couple others--you can download these). To erase, do this:
Just insert a Mac OS 9 or X CD and boot from it (hold down 'c' at startup).
In OS 9 install, just go to the utilities folder on the CD and find Drive Setup, you can use this the erase the hard drive (reformat it).
In OS X install there is an option to reformat the hard drive before installing OS X. This however only erases a single partition. To erase a whole drive, I think there is an option in the apple menu of the install CD to open Drive Setup. Someone please correct me if I'm wrong on that one.
I hope you are not leaving the Mac platform!
Matthew
