Finally got the ATI drivers (went with 8.40.4) to compile and now I've got my workstation running with two monitors, although not quite the way I was anticipating.
Instead of the desktop spanning both monitors, I've got separate desktops on each monitor. It's not the usual desktop layers either. More like having two separate simultaneous login sessions going. Not quite what I was expecting.
Going to have to do a little more research on the matter, but at least it's working (kinda).