The compile script is as follows:

./configure \
--mandir=/usr/share/man \
--with-apxs=/usr/local/apache/bin/apxs \
--with-config-file-path=/etc/httpd \
--enable-magic-quotes \
--enable-bcmath \
--enable-calendar \
--with-dom=/usr/local \
--with-zlib-dir \
--enable-ftp \
--with-mysql=/usr/local/mysql \
--with-pgsql=/usr/local/pgsql \
--with-expat-dir=/usr/local \
--with-sablot=/usr/local \
--enable-trans-sid \
--with-regex=system \
--with-swf=/usr/local/openswf \
--enable-wddx \
--enable-memory-limit \
--with-gnu-ld


The system is:
Linux Mandrake 8.0
Apache 1.3.19
glibc 2.2.2
MySQL 3.23.34a
Postgres 7.0.3
libxml 2.3.4
Sablot 0.51
expat 1.95.1

The code that kills Apache is:

<?php
$doc = new_xmldoc("1.0");
$root = $doc->add_root("HTML");
$head = $root->new_child("HEAD", "");
$head->new_child("TITLE", "Hier der Titel");
echo $doc->dumpmem();
?>

I also seem to be having problems with XSLT functions as 
well, but I will investigate that further.

PHP compiles and runs no problem, just seg faults after 
calling above code.

Stack trace:

No stack.
(gdb) run -X
Starting program: /usr/local/apache/bin/httpd -X
 
Program received signal SIGSEGV, Segmentation fault.
var_reset (var=0x4021a29e) at zend_variables.c:43
43              var->type = IS_BOOL;