I've been messing around with my xorg.conf for hours and have had no luck getting myself set up with dual monitors. I'd like to have my mouse fall off the left side of one, and appear on the right side of the other. The closest I've been able to achieve is a clone appearing on the second monitor. I'm using a single Radeon X300se. I'm fresh out of ideas and have exhausted the list of recourses I've found with Google. Any help would be appreciated.

I think you have not exhausted the list of recourses on LQ here There are STACKS of threads and posts on the subject. Do some searching for THREADS or TAGS containing 'twinview', 'xinerama', 'dual monitors' 'dual screens' 'nvidia' 'multiple displays' etc, you get the idea. I guarantee you will find many useful threads.
If you search POSTS by me, using the tag or query 'xinerama' you will get a starting point too; my xorg.conf file is posted in several places around here, which you would of course need to adjust for ATI rather than Nvidia...