I want to use a RedHat rpm Software Package for CentOS 5.6, but I dont know which version of RedHat works with CentOS 5.6.
RedHat 4 = CentOS 4?
RedHat 5 = CentOS 5?
The version numbers correlate between RHEL and CentOS (as Ben Preston already answered). Moreover, due to RHEL philosophy, the ABI should stay the same across all minor number ( .x) versions, so the package compiled for 5.4 should most likely work for 5.5 and 5.6 as well.