Hi, you can add more than one ip address in windows, just double click the TCP/IP properties -> advanvced -> ip addresses.
Does virtual server give each machine its own virtual NIC? If so, you should be able to keep your windows box ip the same, then assign the other public ip's to each virtual machine. As long as the ip's are on the same subnet windows virtual server will bridge all of the nic's for you.
I have used virtual server before, same thing with the client OS running inside and i just assigned it an ip in the existing subnet and all worked fine. I havent got it to hand though so hence im a bit flakey regarding virtual NIC, but im pretty sure its a simple case of configuring the public ip's in each client OS and then you will be good to go.