Are you talking about editing php.ini for use on a DreamHost account, or in general?
That's a very different thing altogether. So to be clear, is he trying to edit php.ini (presumaby to change a setting) or is he trying to use ini_set to change a configuration setting at run time (I assume he is running mod_php)?
If he is talking about this as it relates to the DreamHost environment, it makes a difference what configuration setting/value he is trying to change as well as whether he is running mod_php or PHP-CGI.
Your friend probably ought to take a trip to php.net, and check out:
.. and then ask his question - or just describe what it is he is trying to install/run rather than assuming what he needs to do to make it work.