Download VBoxLaunch, put it in your VirtualBox folder, run the app, and then pin it to your Start Menu or Task Bar to create your custom jump list. From that point forward you can launch a virtual machine by opening the jumplist and clicking on the machine you want to work with.
VBoxLaunch is free and requires Windows 7 with .NET Framework 3.5 installed.
VBoxLaunch [via Addictive Tips] VBoxLaunch Creates a Custom Jump List for Your VirtualBox Machines