Position entity 3d from 2d mouse

I've been trying to convert this wonderful bit of code to work on the X/Z axis (ie. looking straight down on a plane).
At the mo, this is code for X/Y (looking into the distance).

Can you help. Thanks.

; -----------------------------------------------------------------------------
; PositionEntityFrom2D ()
; -----------------------------------------------------------------------------
; Positions an entity at 3D x/y co-ords translated from given 2D co-ords, at
; specified z position. Useful for positioning an entity at mouse x/y position,
; at its current z depth...
; -----------------------------------------------------------------------------
; PARAMETERS...
; -----------------------------------------------------------------------------
; REQUIRED...
; -----------------------------------------------------------------------------
; entity is the entity to be positioned.
; x2d is the 2D x position you want translated to 3D.
; y2d is the 2D y position you want translated to 3D.
; z3d is the * 3D * z depth at which the translation should occur.
; -----------------------------------------------------------------------------
; OPTIONAL...
; -----------------------------------------------------------------------------
; positionGlobal defaults to false, as per PositionEntity.
; camZoom must be set manually if you've used CameraZoom to change it...
; -----------------------------------------------------------------------------

Function PositionEntityFrom2D (usecam, entity, x2d#, y2d#, positionGlobal = 0, camZoom# = 1)
	gw = GraphicsWidth ()
	gh = GraphicsHeight ()
	x# = -((gw / 2) - x2d)
	y# = (gh / 2) - y2d
	parent = GetParent (entity)
	EntityParent entity, usecam
	z3d# = Abs (EntityZ (entity))
	div# = (gw / (2 / camzoom)) / z3d
	PositionEntity entity, x / div, y / div, z3d, positionGlobal
	EntityParent entity, parent
End Function