Same problem using XP/Outlook Express and Vista/Mail for newsreader.

In Microsoft.public.windows.vista.hardware_devices group there are 0 unread
messages
however it shows some number not downloaded.... if I go out and back in even
if a new
message or several show up there is always some arbitrary number showing not
downloaded.
Even if I exit and re-enter group with NO unread message showing there will
still be some
Not Downloaded. Deleting the group not Deleting all messages in this group
and using
Reset does not correct the problem.

Interesting, even when no new message shows up in this group the number
shown Not
Downloaded will change.