I don't know how they did it. But it was in Linux, not Windows. I only mentioned it to counter Josh's point. It was a lot of fancy stuff. They made some minor changes in the driver/HAL to allow it to work. This was only a minor part of their project. But it was a nonstandard thing anyway. It will not work across all cards, so I cannot help you. I just wanted people to know that it is possible. They had supplied different IPs for different MACs for the same card.
Even in the case of virtualization, I believe a similar thing is done via bridging though.
It should be possible in Windows in the same way, but I don't know exactly how to go about it.
The question is, why do you want multiple MAC addresses?
@Josh: A single MAC with multiple IP's is not a true emulation is it? My bad - I said simulation. They were actually emulating, for which they needed to have an exact replica. Hence multiple MAC addresses.