Thanks, I had the same problem, solved with your help. A few helpful details...
As ronthai says, Cloudberry is very useful. Once you've been through the set up on dreamhost, the bucket associated with your cloudfront dreamhost subdomain will appear in S3 when you access it with cloudberry. To set the correct permissions, rightclick on the corresponding bucket under root, choose ACL settings and press the Public (everyone) button, also, tick the box to apply to all files and folders within.
However, it was only after I logged into my cloudfront account on amazon web services and specifically set my index page that I stopped getting errors. Click the distribution, this activates the distribution settings button, click that and in the general section you can edit it to set index.html or whatever it is as the default route object.
Without that step, I had to visit cloudfront.mything.com/index.html specifically. A request to cloudfront.mything.com/ would give a message that said:
This XML file does not appear to have any style information associated with it. The document tree is shown below.
With the delay associated with making changes to the configuration, it took me a while to work that out.