In Virtual PC, this is a straightforward process where in the properties of each VM, there is a shared folders section which allows you to map a virtual network drive to a folder on the host as if you were connecting to it via a UNC path.
In Virtual Server, this is a little more complicated and you have to be careful do as not to disrupt communication of the host or guests for that matter. An important issue is that on any given server, you can only configure 1 gateway. Another issue is that the IP addresses used in the "internal network" as far as the VMs are concerned may belong to the same subnet as your host...
You will ned to make sure that a network exists that makes use of the virtualized hardware of an active network card on your system. If none exist, create a network so that it is selectable.
For the guest on the administration website, configure the network adapter to "not connected" initially so you can start the VM and configure the TCP/IP properties... You only really need to be able to communicate on the same subnet between the guest and host so there are a couple of ways to do this.
1) In the guest once started, configure the TCP/IP properties of the new network interface on the same subnet as your equipment on the live network,
2) An easier way and to limit damage, you could add an IP adress to the TCP/IP propperties of an active network card on the host in a different subnet than the one being used for main communications. In the guest, configure a static IP adress in the same subnet to communicate. You do not need a gateway to make this work...
Now, in the administration website, you can change the properties for the guest to connect the new virtual network adapter tp the network that your host and guest can communicate on.
In this scenario, I assume communication can occur and that there is no blocking, etc... Otherwise that will also have to be taken into consideration.