To disable the Briefcase Icon via the registry:
Hive: HKEY_CURRENT_USER
Key: Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Name: RunSyncApp
Type: REG_DWORD
Value: 0 disable

The executable for the application is %systemroot%\system32\syncapp.exe. If your users do not have update access to the %systemroot%\system32 folder, renaming the application is a good lockdown method.

If your workstations are installed from a network drive or unattended installation, you can prevent the Briefcase icon from being placed on the desktop by commenting out the syncapp.exe line in layout.inf and txtsetup.sif setup files.

Covers installation and support of NT Workstation. If you are just getting into NT workstation, its a good book. If you are experienced NT techie, forget it.