Problem
You already have a project in github, but you want to move it to a different host (ie dreamhost)

Solution
Following the post here that describes how to setup a new git repository in dreamhost, the only difference after the initial setup :

ssh username@dreamhost_domain.com

mkdir -p ~/git/yourproject.git

cd ~/git/yourproject.git

git --bare init

is to edit your project’s .git/config file:
vi local_host/your_project/.git/config

and change the :
url = git@github.com:user_name/project_name.git

to the following:
ssh://dreamhost_username@dreamhost_domain/~/git/yourproject.git

Lastly you have to push for the first time to the server:
git push origin master

Optionally if you would like to check and/or checkout to a different pc you can use:
git clone ssh://dreamhost_username@dreamhost_domain/~/git/yourproject.git