IPSec & Security in an internal network

Hi,

Actually, The data in my network (TCP/IP) travels in clear text and I am trying to find a "hardware" solution to encrypt the information that travels in my internal network. Is an good option to use IPSec inside of my internal network with CISCO solutions? and if the answer is Yes, How? What about NAT problems with IPSec? We have a 3000 Cisco Concentrator VPN to connect remote clients to our network but I am not sure about the application in my internal network to avoid internal hackers. The idea is guarantee the data security between the web servers (located in DMZ), transactional servers (located in the internal network) and AS/400 servers (located in the internal network).

Thanks for your comments,

Marlon Fraile