There are a number of ways to determine the available
drive roots under windows. Would it be possible to
use these for determining the
explorerFileSysRootDefault value instead of requiring
a new user to find then alter this value just to open
a file. The current system makes the "out of box"
experience seem cumbersome.
Alternately, making the standard windows file dialog
the default file dialog would provide the same basic
feature (+ making the app feel more native, providing
or (slower, but doesn't require any extensions):
result = 
for x in range(97, 123):
driveName = '%s:\\'%(chr(x))
if os.path.exists( driveName ):
result.append( driveName )