Certainly post your config file. Also, have you tried making it work in the Big Desktop mode first? There are a few issues with running dual head, mainly due to having to run X on two screens. In my experience, cloning is by far the easiest dual setup so far, and to be honest, I have had little success with dual head.
Just in case you have not seen this yet,
here is a description of how dual monitor setup works in Linux with ATI drivers. Due to two X instances, dragging from one screen to another is not possible as it is in Windows, and there are more limitations to it.