dreamhost does automatic backups of your site. All you have to do to access them is log in via FTP to your acctount and go to the .snapshot directory. becuase it's a hidden directory that won't show up in the list of folders, but if you type it into your FTP program you should be able to access it.
From there you can selecte just how far back you need to roll you site. couple hours, a day, week, or month I believe are all options.
I think if you seach the K-base for Backups you'll find the info.