Tried sending this a while ago, but looks like mailman blocked it?
>But i don't know how to write the spec file so a simple yum update will
>install both packages and it won't create any problems.
A few options here, create a %{name} .spec with:
# This is part one, or the main component
%description
%files
...
%package part_two
Requires: %{name}
...
%description part_two
Smaller part of %{name}
%files part_two
...
Check an example out, one I was using recently to build another was:
https://git.icinga.org/?p=icinga-core.git;a=blob_plain;f=icinga.spec;hb=HEAD
Hth,
jlc