you need something like a "Virtual switch" - generally you will use a second LAN adapter for a different subnet etc.
These sorts of scenarious are used when you have a number of "Virtual Servers" running on a Host machine running a Hypervisor (Vmware's ESXi or Ms's Hyper-V).
These are "bare metal machines" with a really tiny skeletal Linux system in them so maximum resources can be given to the VM. These allow multiple LAN cards to be used for different sets of VM's on different subnets controlled by a Virtual switch.
I'M sure XP mode won't allow anything like this -- you'll in the first instance need to create SEPARATE Virtual Machines, and then have some good virtual networking software to run these with.
Start by reading this -- although I think its overkill for what you need to do it's good learning material. What is Virtual Switch (VSwitch)? A Technology Definition From Webopedia.com