I have one of the "walmart special" halogen floor lamps -- the kind that look like an upside down lampshade pointing at the ceiling. It has a two-level switch (off, low, high).

I use a standard X10 plugin lamp module. It works fine. The problem with Halogens is that they tend to have a short lifetime if they are below a critical temperature. The was I understand it, any material that evaporates from the filament should not plate out on the quartz tube. Presumably, when you turn them off, the filaments will cool faster than the quartz and it will plate back onto the filament. If the quartz isn't hot enough, it plates onto the quartz. So if you run the lamps at a low power level, you lose on lifetime of the bulb.

I haven't noticed any problems with this, and the X10 control works fine with the lamp turned on to either setting.

Joe