You need to create a new CNAME record pointing to Google . Then go to Simple DNS Zone Editor. Select the domain name you would like to setup with Google Docs from the “Select a Domain” drop-down menu. In the “Add an CNAME Record” section enter docs in the “Name” text box and enter ghs.google.com in the “CNAME” text box. Click the Add a CNAME record button. Now at Google Docs, you need to change the Google Docs URL in Google Apps so that you can access it through your domain.
Hope so its fulfill your need!