Error "DOM: NOT OK" checking environment

[PinheiroRJ]

Hi All, help a linux newbie administrator.
I´m trying to install roundcube stable. When I click "Check the Environment" returns "DOM: NOT OK(Could be loaded. Please add in php.ini;".
How to fix it? The PHP version is 5.2.9, Fedora 9 Box.

Four optional extensions are relating "NOT AVAILABLE" (Fileinfo, Multibyte,
MCrypt and GD)

Sorry for the basic question, I´m just a beginner in Linux world.

Tks in advance.
Pinheiro
Brasil.