In November 2007 Apple made a modification to its EULA to allow the virtualization of Mac OS X 10.5 Server. And in these months the two firms competing in this space, Parallels and VMware, worked hard to make it happen.
Parallels will probably offer Mac OS X Server support on its upcoming server virtualization product Server 1.0 (now in Release Candidate).
VMware instead just announced that it will offer that support on its upcoming desktop virtualization product Fusion 2.0 (now in beta 1).
Unfortunately nor Parallels neither VMware can offer a virtual machine with Mac OS X on an hardware which is not Apple branded.