I'm currently adding my private IP's to CentOS5 and was wondering if anyone knows of an easy way to do this as well as what rules do I need to input in to IPTables for my two Linodes to be able to speak to each other via the private IP's?

take a look at firehol as it makes creating rules a snap and handles all the iptables rule creation

I have a tut covering setting this up:

http://gregsidberry.com/2008/10/22/buil ... -security/

hope it helps