I tend to keep a large number of different virtual machines inside Virtualbox. In addition to various Linux distros, I have multiple versions of Windows XP in there. This can get confusing for somebody else using my computer, especially for my wife. I've created a virtual machine with only the software she needs to remote access her employers' mainframe(via Attachmate Extra) and email (via Lotus Notes). I wanted to make things easier for her and put a shortcut on the desktop for her to click on that will start the specific Windows XP virtual machine that she needs.
This example is with KDE 4. Start by right-clicking inside the Desktop folder plasmoid. Then select the 'Create New' option and then 'Link to Application'. You can change the Icon on General tab, but the real action happens on the application tab. In the 'Command' field put the following: kstart VBoxManage -nologo startvm "Your exact virtual machine name here".
This is what the properties look like for my example:
