KVM is 'already there' - it's part of the kernel. (hence "kernel-based virtual machine"). Virt-manager (the GUI and console config tools) is a Red Hat thing, and was there in Fedora 8 and obviously Fedora 9 too, but the latest Ubuntu now has virt-manager too.
As it's part of the kernel, there's not really anything to install.
It's actually a sort of qemu fork, or at least what you use is a modified qemu which ties in with kvm. I remember qemu from the days of experimenting with bochs, and wouldn't have thought of qemu as a 'proper' thing, but kvm is very good. So really, the solution is known as "qemu-kvm". If you don't turn on "hardware acceleration" in the virt-manager stuff, you just get plain qemu which is obviously slower than qemu-kvm ("hardware accelerated virtualisation").
http://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine