This may be "bogus" to you (sorry), but I first heard of your package today and am interested in trying it out. I have tried this on two different RH9 installations (one fairly stock, the other a very up-to-date workstation)without success. I could try to figure it out myself, but
until I get hooked on xdebug I'm lacking enough incentive to hack at it.
=)

I followed the instructions in README. Note the errors from make. I performed (as a non-root user):
$ phpize
$ ./configure --enable-xconfig
$ make
/bin/sh /work/xdebug-1.3.1/libtool --mode=compile gcc -I.
-I/work/xdebug-1.3.1
-DPHP_ATOM_INC -I/work/xdebug-1.3.1/include -I/work/xdebug-1.3.1/main
-I/work/xdebug-1.3.1 -I/usr/local/include/php
-I/usr/local/include/php/main -I/usr/local/include/php/Zend
-I/usr/local/include/php/TSRM -DHAVE_CONFIG_H -g -O2 -prefer-pic -c
/work/xdebug-1.3.1/xdebug.c -o xdebug.lo
gcc -I. -I/work/xdebug-1.3.1 -DPHP_ATOM_INC -I/work/xdebug-1.3.1/include
-I/work/xdebug-1.3.1/main -I/work/xdebug-1.3.1 -I/usr/local/include/php
-I/usr/local/include/php/main -I/usr/local/include/php/Zend
-I/usr/local/include/php/TSRM -DHAVE_CONFIG_H -g -O2 -c
/work/xdebug-1.3.1/xdebug.c -fPIC -DPIC -o xdebug.lo
In file included from /work/xdebug-1.3.1/xdebug_var.h:20,
from /work/xdebug-1.3.1/xdebug.c:55:
/work/xdebug-1.3.1/php_xdebug.h:66: warning: parameter names (without
types) in
function declaration
/work/xdebug-1.3.1/php_xdebug.h:66: warning: data definition has no type
or storage class
/work/xdebug-1.3.1/xdebug.c:125: xdebug' undeclared here (not in a function) /work/xdebug-1.3.1/xdebug.c:125: initializer element is not constant /work/xdebug-1.3.1/xdebug.c:125: (near initialization for xdebug_module_entry.post_deactivate_func')
make: *** [xdebug.lo] Error 1

Obviously I'm doing a clean install, here.