Question : Slow transfer speeds on Gigabit LAN

I have a windows 2003 domain with 50 users and 12 servers. The network consists of 5mps fiber connection, Cisco 1841 router, Cisco 5510 firewall and 5 Netgear GS724TS gigabit 24 port managed stacked switches.  I have not had much experience increasing/troubleshooting network performance issues. My file transfer speeds are slow within the network, especially while performing a backup. The network speed is no faster than the 100mps unmanaged network I replaced. Please Help, I am not sure where to start.

Answer : Slow transfer speeds on Gigabit LAN

I tried wireshark which does scan in very deep detail, but I can only scan the Nic's of the machine that its installed on. I use solarwinds for network monitoring, but I never any nic's that are over 20% utilized. Is there any way that wireshark can use the SNMP data of my switch's so I could analyze the network as a whole?  If it could the main issue I have is what should I be looking for in the data?