Yup, remove old one first!
I recon you had apache installed with rpm and then later compiled it yourself.
When you compile apache, you cannot use /etc/init.d/httpd to start and stop the server. That's because it always will use the old installation.
Do the folowing:
to find out wether you have apache rpm installed:
rpm -qa | grep http
if that gives you a line like
rpm -e httpd-devel-2.0.40-21.3 httpd-2.0.40-21.3
to get rid of old install...
move old config-file
mv httpd.conf httpd.conf.backup
create softlink to new configfile
ln -s /usr/local/apache/conf/httpd.conf httpd.conf
and then go
that should set you up.