DH supports PHP and Apache.
After you have an account, DH will automatically install PHP and MySQL for you. You do not need to do any installation by yourself.
To manage MySQL database, DH provides you PHPMySQLAdmin web panel to communicate with the databases.
I do not know much about Linux but have no problem using the hosting plans.
There are more features. You may want to refer to DH office site http://www.dreamhost.com/hosting-features.html
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