First of all, this is for secureweb-3.1-1 as shipped with RH 6.1 Prof.
I tried enabling both mod_perl and mod_php3 by uncommenting entries in
httpd.conf. The server started and quickly died with no error messages,
nor any log entries.
Believe it or not, changing the order of how the modules load in httpd.conf
so mod_php3 loads BEFORE mod_perl fixed it
I'm not sure what configuration file you are using, but I have just verified
that for Secure Web Server 3.1, mod_php3 is listed before mod_php in httpd.conf.