Hi mrm3,
I've been looking at the Lutron range for a little while, and as far as I know, the Incandescent Dimmer is only suitable for simple incandescent bulbs (mains 230v).
The Universal Dimmer is for use with more complicated loads, like low voltage halogen lamps where the dimmer is supplying power to the bulb through a transformer.
From what I remember, the Lutron web site pretty useful and should list off the types of loads that can be controlled by either the Incandescent or Universal dimmers.
What type of lamps will the dimmer be controlling?
Andy_C