If you've spent the last few days banging your head against a wall trying to get DBG to load with PHP on fedora then maybe this will help.

The symptoms are:
dbg does not load.
/var/log/messages has "avc: denied { execute } for..." showing the dbo.so module
if you try and load dbo manually (dl in php) then you'll see "failed to map segment from shared object: permission denied"
The root cause is SE linux (Security Enhanced Linux: Link: http://fedora.redhat.com/docs/selinux-faq-fc3/index.html#id2763109)
the simplest thing to do is disable is:
setenforce 0
and then restart apache:
/etc/init.d/httpd restart
This is only a runtime solution. For a boot time solution edit:
/etc/sysconfig/selinux
But read the link above, so you set the option best for you.

Hope this helps - it would have saved me the weekend.

Thanks for your report.

Probably, recompiling the module under FC3 will help without modifying SE policy.