The PHP upload_max_filesize directive is set to 7Mbyte in the default DreamHost php.ini files. As others have pointed out, you can change this by following the instructions in the wiki and copying the default DreamHost PHP executable and ini file to your domain directory and configuring Apache to use this local install. The procedure is not too difficult, but you should have a good working knowledge of the shell before attempting it.
Another option would be to use a script written in a language other than PHP (such as Perl), which is not subject to the 7MB limit.
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