In Leopard, although Virtual PC 7 generally works fine, it puts VirtualPCNetworking1040.kext in the Dock, which should be running in the background.
To fix this, open its Info.plist file (probably at /Library » Extensions » VirtualPCNetworking1040.kext » Control-click and pick Show Package Contents » Contents » Info.plist), and add a key of LSUIElement with a string value of 1 just before the final </dict> tag. In a text editor, this would be:
<key>LSUIElement</key>
<string>1</string>
Or you can use the Property List Editor from the Developer Tools to add a new child of the Root with the appropriate key (LSUIElement), class (String), and value (1). Google LSUIElement if you need help using it appropriately; I just wanted to point out that using it will get the kext out of your dock!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080109131926970