The x86_64 kernel 2.6.18-1.2798 rpms are just a rebuild of the stock
Fedora Core 6 kernel downloaded from:

http://download.fedora.redhat.com/pub/fedora/linux/core/6/source/SRPMS/kernel-2.6.18-1.2798.fc6.src.rpm

They were rebuilt, because VMware-server does not work with the 2.6.21 kernel
from Fedora 7.