There is an AppNote on SupportNet about managing Global Signals in DxDesigner, AppNote 10770. You will also find a sample library in the install that has a number of the required symbols defined: look in standard\examples\samplelib and in the builtin library you will find on-sheet, off-sheet and port connectors. Under Globals you will find example power rail symbols, VCC,GND etc. The use of these global symbols with a Property of Global Signal Name = xxxx establishes the connectivity.
To set up the symbols you use got to Setup - Settings - Special Components and then add the correct symbols under each heading.
For more information on creating template projects see my post here http://communities.mentor.com/message/10401#10401
Your reply was very helpful regarding global symbols. However, I'm still mystified by "Hierarchical" symbols. I'm not able to identify any difference in properties between Hierarchical and "Local" symbols. It appears that Hierarchical symbols are nothing more than a local symbol with a different appearance that would be used as input/output terminals with "Blocks" as a reminder that the pins for a "Block" are inherently hierarchical. Is this true? The only evidence to the contrary is a reference that you need to use "Hierarchical" symbols to convert files from 2005.x to 2007.x.
Also, in your App Note 10401 you describe how to create a default project template. However, I'm not able to find the folder structure identified ($WDIR\Templates\DxDesigner\Expedition) or anything like it. Can you help?
I'm not sure that I understand your question regarding hierarchical symbols, in general symbols are of four types, Annotate, Pin, Module and Composite. Annotate are used for symbols such as on/off-sheet connectors and sheet borders, they are used to provide documentation information (cross-references, drawing info etc). They do not get packaged for layout or compiled for simulation. Pin types are used for hierarchical ports and global signals. The hierarchical ports link the lower level schematic to the I/O definition of a hierarchical block symbol, hierarchical blocks are Composite type components, that is they are made up of underlying schematics, generally they're simple hierarchical blocks with connections that traverse from the parent sheet to the child schematic. They are used to drive connectivity and do not have a Part or cell in layout. Module type components are symbols that get mapped to parts and are passed to layout. They are 'PCB' symbols and may have associated simulation models for SPICE or HDL.
On the question of the templates path, when the software is installed each user is requested to set up a writable folder known as the WDIR. It is defined by an environment variable $WDIR, you can work out your WDIR path either by listing your environment variables or from Dashboard (if you use it) there is a node in the navigator that lists the WDIR paths.