i experienced very vexing behavior from php-3.0.{14,15} under apache 1.3.{11,12}.
some details on setup:

redhat-5.2/x86, kernel 2.2.14, all security and kernel-2.2 requirements from
	redhat are the only changes to the stock install.
apache: configured with '--enable-module=all'
php: configured with '--with-mysql'.  (installed separately after apache)
stock php3.ini file copied from php3.ini-dist w/no changes
 
apache works a-ok until i activate the php3 module with the LoadModule directive;
after that the parent (running-as-root) httpd will fork a child, but will itself loop
in sched_yield (according to strace) while the child never does anything (including
get any brothers or sisters).  the parent is at this point eating all CPU and doing nothing but sched_yield'ing

an example strace output is available at: http://www.ticam.utexas.edu/~chrism/php_strace

as httpd never crashed, there is no corefile available.

building php3 into httpd cures the problem, and that's what i resorted to.  this appears
to be the same bug as ID #1043, except that mod_ssl is not involved, and bug #1043
got closed without any apparent resolution, so i am opening another.

again, my problem has been solved by avoiding the DSO setup, but it took me a long
time to get around to trying it and i was about to tears by that point.