Cannot see certain files and folders on Windows 2003 server from V

We recently upgraded (3 weeks) our office computers to Vista. Our server is
Windows 2003 server. Our IT person provides an H: drive to our data storage
area. I have traditionally mapped a couple of drives to subdirectories of
that data drive for the folders I use most extensively, as we have fairly
deep paths at times. This was my practice in XP and it worked perfectly. On
my Vista computer, there are apparently random files and folders that simply
are not visible from these mapped drives. They are visable from the H: drive
as mapped. I also can connect remotely to my old computer where I have an
older copy of Quickbooks which won't run on Vista (until we get our new
Quickbooks). On this computer I can still see the files and folders on my
mapped drive. If it weren't for that fact I probably would never have
noticed that it worked on the H:\ drive as I almost never use the long way,
but after trying a number of settings to "view files", I thought I had fixed
it, but realized that it worked on H:\. My IT consultant has not had time
yet to track this down, but I really need to know at least the mechanism of
the problem, if not a solution.