Migrating a physical machine to a virtual machine can be done a number of ways. You can use System Center Virtual Machine Manager, PlateSpin PowerConvert or a host of other tools. One of those tools is the free Disk2VHD tool from Sysinternals. Disk2VHD will take a snapshot of a running machine and write it to a VHD that you can boot up in Hyper-V (or Virtual PC). The process is pretty straight forward and in Part 1 we captured the source machine. In part 2 we will bring it online in Hyper-V.
With the VHD copied to the Hyper-V Server we simply have to create a new virtual machine. When you get to the Connect Virtual Hard Disk screen simply select the VHD you captured with Disk2VHD.
You will have to make sure all the hardware settings are similar. If you had 4GB of memory on the physical machine the virtual machine will need the same. There are no sizing differences between the physical and virtual machine. You will also need to make sure your CPU settings are similar and that you have the same number of NICs as the physical machine had.
Once that is all verified you can boot the system. Leave the NICs disconnected for now until you verify the system is working, then take the old system offline, connect the NICs and you are ready to roll!