One thing that I thought I'd miss in switching from VMWare Workstation to Microsoft Virtual Server 2005 was the ability to set up a virtual network. What I mean by that is a network that consists only in memory and allows the host to talk to guest virtual machines, and which allows guest virtual machines to talk to each other. Historically this has been something of a pain in the Virtual PC family of tools, but in Virtual Server 2005 it's a snap to set up.
First up, make sure that you have the Microsoft Loopback adapter installed. To check this go to the control panel, and check your network connections. You should see a virtual network adapter in there based on the Microsoft Loopback adapter. If you don't (it's not installed by default by either Virtual Server 2005 or by the Windows XP installer), you'll need to go to the Add/Remove Hardware applet in the control panel and add it. It's quite painless. When the applet first runs it checks to see what hardware in your machine doesn't currently have drivers set up for it. Once you've managed to skip past that just tell the applet that you want to manually specify the hardware you want to install, go to Network devices and pick up the Microsoft Loopback adapter.
Once the loopback adapter has been installed drop into the Virtual Server 2005 Administration website and choose to create a new virtual network.
As you can see in the screenshot, make sure you connect this new virtual network to the loopback adapter. With that done, click on OK and you'll get returned to the network properties page, looking pretty much like this.
The next step is to enable the DHCP server on the network so that all the virtual machines get a valid IP address. Just click on DHCP server to go to the DHCP server properties page and click Enabled (you really don't need to do any more than that).
Notice how the netmask is set to 255.255.0.0 and your machines will get address in the 10.242.0.16 to 10.242.255.254 range - plenty of scope there for lots of virtual machines. The only problem with this arrangement though is that the loopback adapter for some strange reason won't pick up its address from the DHCP server, so I had to manually set the IP address for my host machines loopback adapter, as shown
Now all that remains is to connect one or more of your virtual servers to your new network. To do that, click on Configure in the Virtual Machines task pane and then chooes the machine that you want to add into the network. When the configuration page pops up, click on Networking and use the Network adapter properties page to specify the new network you just created for use in the virtual machine.
That's all there is to it. You can now run your virtual machine and you'll find that not only can you connect to it from the host machine, but it can't talk to any other machine anywhere in the world unless it's the host, or another virtual machine on the virtual network.