I'm having a bit of trouble with RPM dependencies.  I'm trying to package faifa, which manages HomePlug AV interfaces.  There's a library (libfaifa) and two executables, faifa and hpav_cfg.  I'm putting the executables in the main package (faifa), the shared library in a -libs subpackage, and the headers in a -devel subpackage.  I have both the main package and -devel subpackage depending on the -libs subpackage, both using the line:

Requires:       %{name}-libs%{_isa} = %{version}-%{release}