David,
Popped in to respond to your earlier post, so let me give a quick snap-shot.
From cheapest (and least to most improvement)
hub - switch(unmanaged) - switch(managed)
in and amongst switches, you will find layer 2, layer 2 plus, and layer 3.
The layer 3 switches are going to cost significantly more for 24-48 port GIG switches. If you have the room, I'd go with 2 16/24 port switches, and separate the two enterprises into two different network segments and bridge then into a shared segment (8-16 port switch) that has the servers, other shared network resources, and the firewall.
Because of what goes on inside it, a layer 2 GIGABIT Switch (as a minimum) will provide significantly better performance as it reduces network collisions and network contention (noise).
Hope that helps some, if you need additional help, please send a PM, as I'm not able to visit the forum often.
