Insert the equation into a wide figure float:
In LyX 1.3.x: Insert->Floats->Figure, and then press the right mouse button
on the figure frame, and select the "span columns" button.
The question would be: Doing this i have the ugly 'Figure:' caption going around
After you have inserted the figure float, set the cursor behind the word 'Figure' and choose 'standard' instead of 'caption' in the format menu.
