If the pipes come up through the floor of the cabinet, as you indicate, with the water off you remove the valves, (with the water pressure turned off, of course) ect, so you have only the vertical pipes coming up. Measure carefully and drill/bore holes in the bottom of the cabinet where the pipes will come through. (This usually requires any adjoining cabinets on one side to already be in place.) Then lower the cabinet over the pipe stubs and secure it in place.
If you make the holes 1 1/2 to 2 times the outside diameter of the pipes, it will give you some adjustment tolerance. The extra diameters of the holes can be masked with escusions.
Then, reinstall the valves and turn the water back on.
The procedure is not much different for plumbing from the back of the cabinet.