<Setting Id="AllowWindowsClientInstall" Value="True"/>
That is the magic line. It will allow us to install SharePoint Foundation/Server 2010 on Vista and Windows 7 (both x64).
The only missing part is the public beta :-(
Setting Up the Development Environment for SharePoint Server: http://msdn.microsoft.com/en-us/library/ee554869%28office.14%29.aspx