Centos is RedHat Enterprise Linux (RHel) with the logos removed. It runs RHel binaries as well. It is free to download and has a five year support life. Any book written for RH works for Centos. The current release version is 5.1. If you go with any version prior to 5.0 you have about a 1/3 chance of sata being supported directly from the CD(it can be done just with more effort). Fedora is fine (current supported version are F7 and F8) but you only have support for about one year, after that there are no more official updates.