This is usually what I do to get my Redhat box up to date with bleeding edge versions of softwares, while keeping them configured "Redhat way":
I grab the source RPM, extract the .spec file from it, modify it a little bit(at least reflect the version change), and use it to compile RPMs from my new package.
Firstly remove the instance you installed in /usr/local/apache, put your new source, httpd-2.0.45.tar.gz, in /usr/src/redhat/SOURCES, and put the spec file in /usr/src/redhat/SPECS (not required but this is where source RPMs puts them). For your convenience I'll give you mine: http://demonbane.org/httpd.spec
Then you just execute "rpmbuild -bb httpd.spec".
After its finished you'll find bunch of RPMs in /usr/src/redhat/RPMS/i386, which you can use to update your system.
On a side note the cflags rpmbuild uses are in /usr/lib/rpm/redhat/rpmrc, feel free to modify it.