How to expanding environmental variables?

[Austin English]

Howdy all,

I'm working on a automated test for Photoshop CS 2. As before, I'm
trying to do so in a portable way, so it works on various
locales/windows versions (or as much as possible). Because of
wine/windows differences, I need a portable way to get to the shared
documents folder, e.g.,:
Windows XP:
C:\Documents and Settings\All Users\Shared Documents
WIndows Vista:
C:\users\Public\Public Documents
Wine:
C:\users\Public\Documents

Windows has several variables for this sort of thing
(http://msdn.microsoft.com/en-us/library/ms933062(WinEmbedded.5).aspx).
In particular, I need a way to return what %16430% is on the target
system. I've tried using cmd.exe to echo it, but it's not expanding
it. Does anyone know how I can expand this type of variable? I figured
there's probably something in shell32 that can accomplish this, but
nothing popped up at me immediately (and I'm about to run, so I wanted
to e-mail before I leave). Surely there's an easy way and I'm just
overlooking it...

Thanks!
-- 
-Austin