Download the Centos Boot image
Download the Centos DVD image and save it on an NFS enabled share on your lan

Install with Network boot CD

choose to boot: linux text

Choose Manual IPv4
192.168.1.* / 255.255.255.0
192.168.1.*
192.168.1.*

Choose NFS Install

Server: 192.168.1.29
Dir: /install/linux/centos/5.1

Auto install proceeds from here..