Hi Apmuthu
There is no release of 3.1.1 which will run under CentOS 5. The latest release you could run is the last 3.1.0 release which was 3.1.0-146. We discontinued the CentOS work in 3.1.1 and diverted the time to Debian for the S200 platform. In any event, aside from kernel issues, from SARK/SAIL's viewpoint there is nothing in CentOS that gives any advantage over SME
With regard to dependencies, I'm no expert but as far as I know, it is not possible to do an either/or dependency in an RPM SPEC file; you have to do one or the other. In sail we used the env module rpms (smesailenv, el5sailenv) to do a reverse dependency on the sail main release. Once we dropped el5 it made sense to put the dependency into the main rpm, which stopped the possibility of it being installed with EL5, since it wouldn't work anyway.
Best
S