A dimmer switch contains a variable resistor but is slightly more complicated - it takes a 'snapshot' of the sine wave at a certain point dependant on how much voltage you want and hence how bright the light, and therefore can't be used to control dc lights.
Most flourescent lamps can't be dimmed.
If there are 3 terminals on the dimmer then yes, connect to common (may be depicted by a wavy line) and either L1 or L2.
Adam
August 2009