CiviCRM Community Forums (archive)

So at the point you click the install button, you're getting the 404?
Can you go to Help > System Info and make sure your directory permissions are writable.
I almost think a 404 is more an indication of a problem with the J installer tool, rather than the Civi package. Can you try installing another extension and make sure it's working?

Check your php memory_limit setting. Should be 32mb at a minimum.
It's possible the machine is timing out during install (though that usually yields a whitescreen, not a 404).

Where did you upload and unpack the civi package, from which you're now installing from directory?

My experience on Thinkhost, which is fairly similar to DreamHost is that Joomla simply could not install civiCRM the normal way.  I had to FTP the files into place in the administrator directory and install a subset of files with the Joomla installer.  There are precise directions for this around somewhere, although I couldn't find them with a quick search, you probably can.  Lots of people have struggled with this issue, for instance: http://forum.civicrm.org/index.php/topic,4433.0.html

But I gotta tell you - I don't think it's worth it.  I struggled along with ThinkHost for a long time, but they just didn't have the capacity I needed in terms of resources and support.  What I hear is similar for DreamHost.  I just switched to civiHosting.com and the difference is really dramatic.  I'm really pleased so far.  They are $15 a month, but consider that your website is mission-critical to what you are doing and in the scheme of things, extra server costs are small and worth the benefit.  Now's the time to think about this, before you get to far into it.