Although you didn't reference Patrick's original advice on this, I'm sure meant that, as per the Dreamhost wiki page on php.ini, that the OP should use one of the two methods for having your site use a custom php.ini that they can edit and then they should edit those parameters, right? Because as a knowledgeable Dreamhost customer, you know that as this is shared web hosting, we don't have access or control of the shared installation of php4 or php5?
Anyway, so as to eliminate any confusion - Patrick's answer is the first choice for literally getting PHP scripts to upload more than 8M. The other method in the PHP.ini article on the wiki is another method. Note that neither method is supported by Dreamhost. This is important because if PHP becomes unsupported, if you have any problems with any PHP app that you write or any web app that uses PHP, you'll have to in the course of debugging it yourself revert back to the standard Dreamhost PHP before submitting a ticket about it. Well, that's what you should do, though you're free to do whatever you want.
A third and (from me) highly recommended method is that you use Uber-Uploader for having your users upload big files.
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