The directive you are looking for is DocumentRoot. You probably don't want to change ServerRoot because the modules are in there. Make sure the apache config file at /usr/local/etc/httpd/httpd.conf is in /opt/.filetool.lst so it is saved across reboots. If you only need to serve files for PXE maybe consider using lighttpd. It's what I use along with udpsvd for my bootp server to PXE boot my apache server, and it's a lot simpler.