After installing Microsoft Networking with "File-and-Print Sharing for Microsoft Networks", shutdowns could take a much longer time.

A possible cause may be found in the Properties of "File-and-Print Sharing" in your Network-applet in the Control-Panel.  On your desktop, right click on the Network Neighborhood icon and select Properties.  Then find the "File and printer sharing for Microsoft Networks" entry (you may need to scroll down to see it).  Select it, and then click on the Properties button.

Check the parameter/value of "LM Announce".  If it is on YES, then you've found the problem !

LM stands for "Lan Manager", which was one of Microsoft's first attempts at networking (still used under DOS).  This Lan-Manager Announcement option is required to make Windows 3.11 (W for W) or Windows 95 systems visible to old Lan-Manager system.  However, in the more recent/modern networks WITHOUT any Lan-Manager system (i.e.; Windows 3.11, Windows 95/98 and/or Windows NT), there is no need for this.  If it's turned on, it's probably the cause of the long delay in shutting down Windows.

Turn this option off by setting "LM Annouce" to "No".