For the benefit of everyone who has been anxiously awaiting a solution to the problem I posed above on May 9 (both of you), I've found the following workarounds for most navigation needs in Word when doing an Open or Save As... command (these work at least in Mac OS 10.6.8):
(1) To go UP the hierarchy of volumes and folders, press Command - [up arrow key].
(2) To go DOWN the hierarchy of volumes and folders (that is, to open a volume or folder that you have selected), press Shift - Return.
Examples of how to use those moves:
After you trigger Word's “Open” or “Save As...” command, press Command - [up arrow key] a few times to get to the root level of the network, drive, or whatever you are working in. (How many times you need to press that combination will depend on how many levels it contains. But if you are making a macro to do this, have it do that key pressing several times—because once you get to the root level of the network, drive, or whatever, pressing that combination more times does nothing.)
Press Tab three times. This normally results in selecting some volume (or folder) at the root level.
To select another volume (or folder) at the root level, type the first character(s) of its name, or press the [up arrow key] or [down arrow key] as appropriate.
To open a particular folder within that volume (or folder), type the first character(s) of its name to select it, and press Shift - Return; repeat as needed until you get where you wanted to go.
If anyone else likes to use macros to reduce effort in this way, and discovers any better ways to do such things, please add to this thread.