Patricktan gave you the general idea; that is pretty much the process on most such installs.
I have not dug into the Moodle documentation enough to know what "special" php configurations might be required for Moodle - though I know there are many users on the Moodle forums using Moodle on DH. I think they would be a better source of that kind of info than I would .
I suggest running a phpinfo() program from your domain space to see how things are set up by default, and then compare that with the documentation.
Should you find that you need, or want, to customize any PHP settings, you can customize your PHP settings or install your own custom version of PHP5 (or a custom install of PHP4) as needed.
Really, the Moodle documentation and the Moodle forums should give you all the info that you need - I can't step you through it step-by-step.