A PPP guide can be found here: ATLAS PPP Endpoint Creation. It's fairly similar to the Frame Relay configuration, except for the Frame Relay specific configuration. The guide specifies the ATLAS 550, but the configuration is the same for any of the ATLAS products.
One thing to keep in mind, is that the ATLAS only supports IP Routing, and does not do Bridging. So the IP network off each interface will have to be different IP networks.
Hope this helps,
Thank you so much for this! We are setting it up now and it is looking much better!