1. Shut down the virtual machine in Windows Virtual PC, so to exit the Windows XP Mode.
2. Open a command prompt window with elevated privilege.
3. Run the following command
cd /d "%localappdata%\Microsoft\Windows Virtual PC\Virtual Machines"
REM make a copy of the configuration files
copy "Windows XP Mode.vmc" "Windows XP Mode.vmc.backup"notepad "Windows XP Mode.vmc"
4. Modify the number in the following sections. For example, you have a computer that has a resolution rate of 1280x800, you can adjust the following numbers to 1024x640 in the ratio of 16:10. This makes Windows XP Mode display more properly in Windows mode. "<resolution_height type="integer">768</resolution_height>"
5. Save the configuration file.
6. Restart Windows XP Mode
_Contributed by Sharp Xu
It is resetting back to the original resolution, once restarted. What to do?
It appears that the horizontal resolution is limited to 2048. I just brought up a 2560x1440 DisplayPort monitor, and got a useful vertical, but setting the horizontal to 2400 resulted in it snapping back to 2048.