Global signals in DxD are very similar to those in DC with the exception that you don't need a globals file. They're based on the concept of 'TAP' symbols much as you have in DC, they're basically Pin Type symbols with a Global Signal Name = xxx property that defines the global signal. They're stored in a symol library in the Central Library (same as DC) and may be instantiated directly from the CL-Symbol View of DxDataBook. However, you can configure the list of available symbols for each power, ground, in, out etc via the Special Components section of the Setup - Settings Dialog. Select the object you want to set up, lets say Power and then use the New button and browse to the associated library symbol, let's say VCC. Add this and it gets written to the speccomp.ini file in your project directory. So you need to create the Global Symbols in your library and then point to the in the Settings dialog which will populate the speccomp.ini file. Take a look at the sample library delivered with the install at 'Mentor Install Location'\SDD_HOME\standard\examples\SampleLib2007. See this thread too: http://communities.mentor.com/message/10401#10401
Also refer to the DxDesigner Reference Manual in the InfoHub for details of the support files rather than the User's Guide.
Thanks for your reply and "reset".
I keep trawling through all the differences between DXD and DC....