What's the software?
I would provide the spec's from the slowest processor, even though they work out to be close enough to each other when you factor in the difference in amount of cache each of the two processors have. I've yet to hear of any software that would require more processesing power than provided by even a single core from one of those processors.
I would also go with the above recommendation of starting with one vCPU on the VM. You're better off going with one, adding a second later IF you find you must. Software vendors that don't take into account virtualization technologies when listing their spec's are falling behind the times. 2GB of RAM is probably a good start, although you could probably even trim that down to 1GB without ill effect. The beauty of using ESX is (depending on the VM's OS) you can enabled the hot add of both processors and memory to adjust faster.
I would enable the alarms for CPU and memory usage on your vCenter Server (of the VM's). That way you'll know when a VM needs more resources than you've provided it, and can adjust the configuration accordingly. If I was running the X5460 processors, I would probably only have one assigned per VM on my host. Since I'm not (running two E5405 Xeons) I've given almost all VM's two vCPU's... That's only after running with 1 on pretty much all of them (except the vCenter Server VM) and enabling the alarms so that I knew that they needed more often enough to make it worth it to add another. I have no VM's with more than two vCPU's assigned. That includes an Exchange 2010 server (which is the only server I've given 4GB of RAM to).
VMware VCP4
Consider awarding points for "helpful" and/or "correct" answers.
