Configure line:
./configure --with-pgsql=/usr/local/postgresql \
                --enable-trans-sid \
                --enable-track-vars \
                --with-pspell \
                --enable-bcmath \
                --enable-calendar \
                --enable-ftp \
                --enable-wddx \
                --with-curl \
                --with-imap \
                --with-mcal=../lib-src/libmcal-0.6 \
                --with-xml \
                --enable-sockets \
                --with-apache=../apache_1.3.12

The problem is with the sockets module, really.  Here's the relevant output from make:

Making all in sockets
make[2]: Entering directory `/home/drewpc/php/php-4.0.2/ext/sockets'
make[3]: Entering directory `/home/drewpc/php/php-4.0.2/ext/sockets'
gcc  -I. -I/home/drewpc/php/php-4.0.2/ext/sockets -I/home/drewpc/php/php-4.0.2 -I/home/drewpc/php/php-4.0.2/main -I/home/drewpc/php/apache_1.3.12/src/include -I/home/drewpc/php/apache_1.3.12/src/os/unix -I/home/drewpc/php/php-4.0.2/Zend -I/home/drewpc/php/php-4.0.2 -I/usr/local/include -I/home/drewpc/php/lib-src/libmcal-0.6 -I/home/drewpc/php/php-4.0.2/ext/mysql/libmysql -I/usr/local/include/pspell -I/home/drewpc/php/php-4.0.2/ext/xml/expat/xmltok -I/home/drewpc/php/php-4.0.2/ext/xml/expat/xmlparse  -DXML_BYTE_ORDER=12 -g -O2  -c sockets.c && touch sockets.lo
sockets.c: In function `php_minit_sockets':
sockets.c:189: `MSG_WAITALL' undeclared (first use in this function)
sockets.c:189: (Each undeclared identifier is reported only once
sockets.c:189: for each function it appears in.)
sockets.c: In function `php_if_connect':
sockets.c:875: warning: assignment from incompatible pointer type
sockets.c:900: warning: assignment from incompatible pointer type
make[3]: *** [sockets.lo] Error 1
make[3]: Leaving directory `/home/drewpc/php/php-4.0.2/ext/sockets'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/home/drewpc/php/php-4.0.2/ext/sockets'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/drewpc/php/php-4.0.2/ext'
make: *** [all-recursive] Error 1

Here's the RCS id from sockets.c:

/* $Id: sockets.c,v 1.9 2000/08/23 13:47:00 eschmid Exp $ */