Regard QuickBooks Server - yes, its a separate app that is included with your copy of QuickBooks (its on the install disk or disk image).  Run that on the server machine then choose File->Open in that app and open your company file (which is local to the server machine). 

Anyone running QuickBooks on your network will see the shared file.  For the first time have them launch QuickBooks while holding down the option key or else it will automatically load the file the old way.  Once they do that they'll see a shared files section in the No Company Open window.  Then they can connect that way - its much safer.