the real question is what's the db residing on?
could be the slow response to the db is because of the system that it resides on.
In simplistic terms this is the difference between a "hub" and a switch.
a "hub" if what you use is a "hub", broadcasts that it has packets to all computers. It's up to the computer to say "hey, that's mine". So to reinterate, the disadvantage to a hub is that it must send traffic to all computers that are connected to it to find out where the data goes to
A switch is smarter. A switch creates a MAC address table and knows which computer is connected to which port. It then reads the packet and forwards the packet to the correct computer substantially reducing the amount of traffic on the network.
Linksys advertises their switches using terms such as "a hub". That shouldn't be confused with the switch actually being a "hub".
I can't imagine that the network isn't already cabled for CAT 5. What cabling is it now? CAT 3? CAT4? CAT 3 is typically telephone and CAT 4 was used in Token Ring networks.