Do you actually need any of them? What do you plan to do with the Virtual Machine anyway? That may help people answer your question. Also Vista is the only one you listed there that you can still buy as far as I'm aware, but if you can get hold of ME you could relive the horrorrs of it just for fun lol.
I would go with XP if it it not your main OS (which I think it is) but some f those listed cannot be bought anymore. If XP is your main OS then get Vista or Windows 2000.
I say non of them, XP can and does support anything thats been made for any of those OS's listed. I run Linux in a VM and load it once in a blue moon if I see a linux only program that I want to check out.
If anything just virtualise XP and mess around with it to test it's limits. Download anything, go on any site, see how easy it is to infect a Windows machine lol. Best thing with VM is it'll keep it seperate from the rest of the system so it's all safe.
A virus can move outside the VM environment if the infection is present when the VM is shut down. Dont forget that data is STILL on your HD and when you close the VM there is no longer that berrier in place.
Only good thing I can think of for running a windows OS in a VM is to try and cause self made problems to trouble shoot a problem you have on a clients computer.
I use to do this all the time when I faced a problem that I could not figure out on a clients machine, I would try to recreate it on another computer, thus allowing me to know what was done to cause it, and know the reverse steps to solve it.
Most of the time a computer problem can be fixed by simply reversing what you did to cause it to happen in the first place, and which is why we always ask "What were you doing when it happened?"