But I never seen you complain about the mercedes application not working. 
It is just that you like to see a start button? I'm not sure I understand if it is actually a problem as it seems like mercedes has intentionally removed the start button.
The only supported ways I found for removing start button and a lot of applications from the start menu was using microsoft's group policies.
See for example here: http://support.microsoft.com/kb/292504
The other virtual machine you are talking about uses Windows 7 builtin virtualisation, aka Windows XP Mode?
If so then that virtual machine could be imported into VMware's Player.
re. starting/installing another virtual machine. Normally a recent VMware Player (i think starting from version 4, we're at Player version 5.x now) will allow you to create a new virtual machine from the File menu. File -> New
But if mercedes has locked down the Windows image, they might also have done so with VMware Player. It is difficult to say without seeing it myself.
All of that to stay within the licenses they arranged with Microsoft and/or VMware.
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Wil