Well, it depends what you mean by "etc."
As well as the OS 9 and OSX cd, the iMac came with a restore disk that had the included applications (or perhaps several CDs) If you reinstall the OS, you'll also need to reinstall the bundled applications separately.
Your emails, data files, user accounts, music,, photos etc. will of course be deleted when you reformat, as will any third-party software AND any Apple OS upgrades, you have to bring it up to date through Software update. (This can take a long time if you are on a slow Internet connection).
Thanks
Trevor
CanadaRAM.com