Yeah, I later found some pictures of some DL380s laid out like that and I was like "Yeah... it's probably just windows." VMWare ESXi/ESX/VSphere is pretty cool. My newest machine is a Dell PowerEdge T610 (which is, as I understand, sort of like something HP would sell with the ML brand) and runs ESXi. It's pretty awesome and nearly infinitely expands the usefulness of the machine. Right now I have Solaris 10, Windows 7 and Windows Server 2008R2 running on it with "just" 4gb of ram. (At some point, more ram is going to be one of my first updates to the box.)

I've heard rumors of OS X on ESX/ESXi, and know a person who runs it this way on his Dell PE 2950, but decided against doing it this way myself because my box was mainly for VDI experiments (and replacement of desktops and the previous server roles) -- not necessarily to run OS X desktop software, which VMWare is bad at.