Hyper-V Program Manager
Under Virtual Server we give you the ability to create multiple private virtual networks for use by your virtual machines (this is very handy for creating complicated, but isolated, networking infrastructures). Unfortunately under Virtual PC we only provide one private virtual network.
This can be easily remedied.
All you need to do is to install as many Microsoft Loopback adapters in the physical computer as you want private virtual networks (the details on how to install the Microsoft Loopback adapter are provided in the Virtual PC help files; to install multiple Microsoft Loopback adapters you just have to repeat the process). You should then unbind everything but the Virtual Machine Network Services drivers from these new loopback adapters (unless you want the host to be able to join in on the networking - in which case you can just leave them alone) and launch Virtual PC.
The only problem now is that you will have a bunch of virtual networks with names like "Microsoft Loopback Adapter #5" - but this can be easily fixed by following the process outlined in my post yesterday.
N.B. If you do decide to leave TCP/IP enabled on the Microsoft Loopback adapter you should configure it to use a static IP address; otherwise there will be a noticeable pause whenever you first login to your physical computer as it attempts to get a DHCP lease on the loopback adapter (which will never succeed)