You can try setting  up the security settings for portal  content
folder and dashboard folder by removing all users accept the
administrator. In doing this the folders  would only display in the
document library  if you are log on as an administrator. Just make
sure that you removed all other users.

There are a couple of ways to achieve this (such as setting  the
IsHiddenInPortal property on those folders  you do not want to appear)
but the easiest would appear to be modifying TahoeUtils.asp in the
portal/resources folder as follows (after taking a copy of course!).

'+Start customization
' g_strSavedFolderPath = "/" & GetWorkspaceName()
g_strSavedFolderPath = "/" & GetWorkspaceName() & "/Documents"
'-End customization

Note I haven't exhaustively tested if there are any side effects of
doing this but it seems to work ok!

Be careful about using security settings on the portal  folder. Especially if
you use the News, Announcements, Quick Links, & Resources folders. We keep all
our style sheets and icons in the Resources folder. If you lock them out, they
will be asked to enter the ID and password. Of course that won't work and
they'll get frustrated because the page  won't load correctly.

I had the same question and found it asked and answered in the SPPS
newsgroup on the microsoft site. It is in the general section, page  17
and the topic heading is "Change the document  library link". There are two
answers. I'm not the tech person here and have not yet asked those who are
to implement this, so I can't tell you if the answers are good or
not. The link to this page is
communities.microsoft.com/.../default.asp
I hope it works! Tell me, please, if there are any glitches.