I have done this with a UPB UMI, motion sensor and a PC.  While functional there is a noticable difference on local control.  With X10 Floodlights the light comes on immediatey on motion detected, but with the UPB motion in, processor, UPB relay out transaction it adds a second.  Not a problem when walking, but when a car is moving there is quite a bit of distance covered by the car before the light comes on.