How to Create Differencing Disks in Windows Virtual PC
"A differencing disk is a virtual hard disk you use to isolate changes to a virtual hard disk or the guest operating system by storing them in a separate file. A differencing disk is similar to the Undo Disks feature because both offer a way to isolate changes in case you want to reverse them."
This will need a already set up Virtual PC vhd to work.
Virtual PC and XP mode is in beta and as always can crash and corrupt data inside the VHD (Virtual Hard Drive)
1. Have a vhd created or have XPM installed...
if you have and have setup XPM and can log in then you are set...
2. Open the Virtual PC Wizard...
1. Either type vpcwizard and go to step 2
2. Or go here...
then click on Create Virtual Machine
3. Type the name of the of the new VM and click next
4. Type how much Ram you wish to let the VM access
and if you do not wish to let the Computer Access to the network unclick on the checkbox and click next...
You might need to pay special attention to the Use Computer Network Connections if you have scenarios where its an infected computer, since it might propagate through the lan and connect to the Internet. If you want a isolated scenario then untick the box
5. Click on the "Create a vhd using advanced options" and if you want to at any time reverse the any of the disk activity then click on "Undo Disks"
"Undo Disks is a feature that saves changes to a virtual machine’s data and configuration in a separate undo disk file in case you want to reverse the changes."
Compared to Differncing Disk this is a Short-Term approach to Isolate a vhd.
6. Now choose the Differencing Option
7. Now type the Name of your vhd that will hold the differences and if you want to create it in a different location you can do so now...
8. Now point the install to where you you have the original vhd with the original vhd
Now heed the warning when it says that if you boot the main vhd and if you do any actions on that vhd this VM will become unusable...
If you dont want to create another vhd then this tip should work...
If you have XPM then just make a copy of the Virtual Windows XP.vhd file and then use that....
9. Now you have an Isolated VM which is making its changes to your new vhd....