I sent this to a buddy of mine so he could set up his domain to point towards his Posterous blog, and I thought maybe someone else might benefit from it as well.
If your domain is registered through Dreamhost, this is how you set an A record towards your Posterous blog.
Go to the “Manage Domains” section of http://panel.dreamhost.com
Add the A record as shown. I used a subdomain, but you could use your primary domain name, as well.
For the subdomain, I entered “blog” in the “Name” field.
“Type” dropdown list should show “A”.
“Value” should be: 184.108.40.206
Click “Add Record Now!”
Once Dreamhost is setup, you can modify the settings for your Posterous blog to use that domain (or subdomain.)
Go to the settings for the blog you’re setting up. With the new Posterous “Spaces” layout, you’d click on “Spaces” in the top menu, then click the gear icon next to the blog you want to change, then “Space Settings”.
Click the “Edit” button.
Mine is already linked, but you’ll see where to enter the domain (or subdomain.)
Once it’s entered, click “Save Settings” and wait for DNS to propagate.
More information can be found on the Posterous help pages: http://help.posterous.com/setting-up-a-domain-with-a-third-party-regist