Sun is laying a third bet at the virtualization roulette wheel besides its yet-to-be-announced Xen-based xVM Server and whatever it does with its shiny new open source VirtualBox desktop virtualization acquisition.

This one's a centralized desktop virtualization scheme, an upgrade of the Sun Secure Global Desktop Software that Sun got when it acquired the Citrix-like Tarantella Inc, which was what the old Santa Cruz Operation morphed into after it sold Unix to Caldera and Caldera became SCO.

It’s called Sun Virtual Desktop Infrastructure (VDI) Software 2.0 and it’s supposed to establish and manage virtual desktop sessions created by third-party virtualization widgetry like VMware Infrastructure 3 on XP, Vista, Windows Mobile, Linux, Solaris and Mac OS X.

These more secure virtual desktops are then what the corporate PCs or Sun’s own smart card-based Sun Ray thin client would access over nearly any network connection.

The difference between VDI 2.0 and its predecessor is a connection broker or Virtual Desktop Connector that brings VMware, say, into the picture and dynamically assigns users to any of a template-based pool of virtual machines – generic stuff like an “engineer’s desktop” or “accountant’s desktop” – or, in the case of some power users, say, the one they always use.

In the VDI architecture IT gets to manage the software and the data from the data center and define policies that govern the virtual machine’s lifecycle. There’s no software on the client device. And users can access their desktop from any machine via the corporate network.

It’s supposed to cut operational costs and make the world a safer place while making employees mobile. Sun hopes it sell more Sun Rays.

The menu of choices includes desktop environments hosted on Windows Terminal Server or Unix-base hosts either on the physical hardware or through virtualization.

Sun’s ready to sell the stuff immediately and there’s a free trial available at www.sun.com/software/vdi/get.jsp. But it’s not open source. The widgetry is priced at $149 per concurrent user with a year’s worth of service.