hal-0.5.9-5.fc7 HAL doesn't seem to support Dell's Ambient Light Sensor. It can be used, in hardware, by pressing Fn+Left arrow (auto brightness), and it will adjust the display brightness automatically.
Created attachment 153411 [details] lshal.txt
Can be solved by writing an addon implementing this interface http://people.freedesktop.org/~david/hal-spec/hal-spec.html#device-properties-light-sensor I did that in one day for my Macbook Pro... It's probably better to track this upstream; care to file a bug at fd.o and close this as UPSTREAM with a reference to that? Thanks!
Filed upstream at: https://bugs.freedesktop.org/show_bug.cgi?id=10760