KVM is a Kernel-based Virtual Machine driver. It relies on Intel VT or AMD-V hardware and does full virtualization. As of late 2006 it is pretty new code, but it is already available in kernel packages for OpenSuSE, Debian and RHEL-RT.
More information on KVM can be found on http://kvm.sourceforge.net/
[wiki:KVM/Performance Here] are some early performance numbers with KVM on an AMD processor.