If you want to split a 4 sided surface (quad) into two, first use Surface->divide (to make 4 quads from a single quad), then select the pairs of surfaces and use Surface->combine to make them into a single surface.
You need a licence to use booleans (and other plugins) but you can see what it's capable of at:
http://www.ac3d.org/ac3d/newin4
Andy