Performance issues with Virtual PC on laptops

If your Virtual PC runs in slowmotion try the following:

a. Stop running Virtual PC
b. Open notepad
c. Open %appdata%\Microsoft\Virtual PC\options.xml (appdata is a hidden directory)
d. Add or edit <.virtual_machines.> section of the file and add this key:
<.enable_idle_thread type="boolean">true

eg. It should be on the same level as the node
(just put it after the last <./virtual_network.> node)

<.virtual_machines.>
<.enable_idle_thread type="boolean">true<./enable_idle_thread>
<./virtual_machines>

f. Save the file and exit notepad
g. Start Virtual PC
h. Don't forget to remove the dots in the XML above

Source: Virtual PC Guy's WebLog