Trouble installing Snow Leopard Server on my iMac?

I'm trying to install Snow Leopard Server on my iMac, which surpasses all of the minimum requirements. I kept receiving the message, "Snow Leopard Server cannot be installed on this machine". I did my research and I tried partitioning my Macintosh HD and putting the source on the new partition. When I restart the computer, I am able to launch the installation, but I kept receiving the message, "Mac OS X can't be installed on this machine because there is a newer version"... so then I erased the HD and tried it again, but I get the same message. Do any of you have an idea of why this is happening?