When using default php provided by dreamhost, you can't access the php.ini file. Becuase of the shared server enviroment, your changes would effect everyone else. That being said, if you install your own php (instructions in the wiki) you can edit the php.ini file and turn url fopen on.
A better system would probably be to change the script's coding to use curl instead of url fopen. Scjessy (simon) has posted some good information here and in the wiki about converting to curl. If you convert the scrip to use curl instead, it will run with the standard php install - and be more secure.