Leopard + “Spaces” isn’t due out until the fall, and for all of my searching I’m not finding any open source virtual desktop code that has been updated within the past 2 years. The last one I tried didn’t allow me to drag things from one screen to the next, which is a deal-breaker for me.
I’ve seen a decent one installed on a former cow-workers MacBook Pro about a year or so ago, but have not been able to find it to save my life. It used the visual of a turning cube when moving from one virtual screen to another. This particular cow-worker did not have his mac tricked out in anyway. No boot camp, no linux.
Both of these let you use a turning cube as a visualization (among other things), but neither allow you to drag windows from one desktop to the next - you have to use a keyboard shortcut, or minimize-switch-maximize.
I don’t even know of a Unix desktop manager that lets you drag from one desktop to the next, if that’s what you meant - although both of these let you drag windows from one screen to the next (if you have multiple monitors).
Development on both of them has ground to a halt, since with the impending release of Leopard there isn’t much point.
I used WindowMaker on my old Debian and Redhat boxes, and I do not recall having any issues with moving existing windows from one virtual desktop to the next. Seems that I took that functionality for granted as being integral to virtual desktops.