Well I have no problems with regexps...
(CentOS 3 s390 or CentOS-3 s390) should both work and you should only
but this doesn't look like a regexp to me...
maybe "CentOS 3[- ]s390" instead?
or "(CentOS 3 s390|CentOS-3 s390)"
or "CentOS( 3|-3) s390"
or "(CentOS 3 s390|CentOS-3 s390)"
etc...
Cheers, MaZe.