UNIX for Dummies Questions & Answers

I have 2 Dell Poweredge 1950 servers running . I have been having intermittent performance issues with the NIC cards on one of them. The two servers are identical and are running the same operating system. The server that has the issue is on the DMZ on a a static IP and is hosting a website. THe issue is, that any network related activity becomes very slow at times. When I connect to the server, the ssh tunnel taken time to establish, if I do pings it takes time to bring up the response. However, once I am on the box, things fly! At the same time if I do the same pings and run the same networking commands on the other servers in the DMZ, they are responsive - the pings themselves don't take time... but there is a long lag between the time I execute the command and the time the response displays. Please advise.
OS: CentOS release 4.5 (Final)
Ethernet controller: Broadcom Corporation NetXtreme II BCM5708 Gigabit Ethernet (rev 11)
Linux version 2.6.9-55.ELsmp (mockbuild@builder6.centos.org) (gcc version 3.4.6 20060404 (Red Hat 3.4.6-8)) #1 SMP Wed May 2 14:04:42 EDT 2007