It's been a few years, but I've done bonding on both RHEL and Cent. It's non-trivial, but fairly straight-forward when following the docs. Just be sure to understand each setting as you're making it.
Here's a good doc on it:
http://www.linuxfoundation.org/en/Net:Bonding
You want to use "active-backup" or mode 1 (they are one and the same). That provides a fail-over if one of the NICs (or the cable it's using, or the port on the switch) dies.
The Cliff's notes version is that you find the mac of both interfaces, then you make a new bonding interface & tell it to use mode 1, then you tell the actual NICs that they are slaves of the bond.
edited to add: I always make a backup of the entire network dir before starting. I forget where that dir is on RHEL - /etc/sysconfig/network?