Can I erase my hard disk with a quick keyboard command on startup?

[seenew]

I'm trying to reformat my HD on an old G3 iMac, but all I've got is Drives Setup or whatever, that comes on the iMac Install CD. I've already deleted all the files from MacintoshHD.. When I try to initialize it, since it says it will delete all data (thats what I want to do) it does it. Then when I try to instal OS 8.5, it says the disk is messed up, and it reverts back to how it was before I initialized it... shouldn't that be impossible?