In the most recent versions of php4 (4.0.4+), something broke, so php4 causes a floating point exception upon startup:
#0 0x80b5cb1 in php_minit_crypt (type=1, module_number=2) at crypt.c:109
109 srand48((unsigned int) time(0) getpid() (php_combined_lcg() * 10000.0));
I don't know what has changed in the php source tree, but 4.0.3 does compile and run under FreeBSD 3.2. shrug