Installing PHP extensions on Linux

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http://serverfault.com – Please bear with me; I'm a developer, not a server admin. My company wants to explore using Magento. They've handed me a pre-configured Linux server with apache and PHP installed, but when I try to run the Magento setup, it tells me that there are PHP extensions that need to be loaded. I can edit the php.ini file, but have no idea where to get the extensions or how to install them, and there's no one here who knows, either. Can anyone give me a hand? I need the PDO_MySQL, mcrypt, and GD extensions. I've searched and found sites that talk about downloading from the terminal and compiling code, (HowTos)