I've never tried using 'bog standard' low energy bulbs with dimmers but I'd assume that attempting to dim the bulb from maximum would initially produce a slight (if any) lowering of the brightness but then, when a critical cut-off voltage was reached, the bulb would simply go out.
However you can now buy dimmable low energy bulbs anyway. They're more expensive than the ordinary ones but, as they're now becoming more widely available, prices will probably start to drop:
http://www.energybulb.../Dimmable+Light+Bulbs
Chris