Wiping HD and installing Tiger

I have a 40GB flat screen imac. I have backed up all my files and am ready to erase my HD and upgrade from Panther to Tiger. But whenever I put in the Tiger install CD (it is used and a little scratched), whether it is off, logged out or logged in, the computer spits it out. I was trying to re-boot it with the CD inside while pressing C and of course it kept spitting it out.

Is this because it is not operating on Tiger right now, or because the CD is bad? Is there no way to erase the HD without an install CD?

Thanks

Welcome to Mac-Forums, foxycoxy.

I see two possible reasons for the CD being ejected. One being, yes, that the media is damaged and the system cannot detect a valid installer on it.

The other being you are trying to use an install CD that came with another Mac: these disks are model-specific and cannot be used to install the OS on another Mac.