A couple of years ago i researched this as i came accross the same options when i was looking to buy a licence for a new employee. Here is what i was told:
Stand-alone is one CD with one licence
Multi-seat is one CD with either 5, 10 or 25 licence depending on how many you need (check amazon.com for prices)
Network licence is one CD and one licence but installed on a network, and when someone accesses the network Autocad from their workstation, the licence is assigned to that workstation for the time it is being used, and cannot be accessed during that time by anyone else.
Hope that helps.