>In a multi-user (medical) application, I would like to put shared-data on a server, in a folder not accessible by clients using Windows-explorer. In this way it becomes impossible to damage, destroy, ..., the data, by the users themself.

One kludge I used at a site was to remove the FileScan rights (Novell server). The users could go into explorer, but could not see the files. However if they know the file name, they can delete them. This adds a bit of oops security, but does not completely protect the files.