A new beta build of Parallels Server for Mac has been released, which supports running virtualized instances of Leopard Server. The result is that multiple copies of Leopard Server can be set up, with each configured for specific applications to maximize available resources.
The ability to run Leopard Server was actually found in earlier private betas. It was taken out though, while technical issues were resolved and performance and stability were being optimized. You will first need Leopard Server to run a virtual copy of itself though.
While Parallels Server for Mac runs on Tiger Server and can host a variety of x86-based OSes, only Leopard Server can host a Leopard Server VM. And Leopard Server is the only version of Mac OS X supported in a VM. According to Rudolph, measures are in place to prevent creating a VM and loading any Mac OS X client version or previous Mac OS X Server versions. The problem isn’t technical; as usual, it is due to Apple’s licensing restrictions.
It is unlikely that the ability to virtualize Leopard is any incentive for IT departments to purchase Leopard Servers. Still, it is a nice bonus for those already running one, or who are in the process of acquiring it.