Magic quotes being disabled is normally a good thing, because it gives you control over whether or not quotes are escaped. If Mambo needs magic_quotes_gpc to be enabled, your best bet would be to install your own copy of PHP5, and then edit the php.ini file to suit your needs.
A more robust solution would be to contact the creators of Mambo and ask them to consider patching their application so that it doesn't need magic quotes to be working. Good luck with that, though.
Simon Jessey | Keystone Websites
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