Not certain - I don't use Truespace. In general, any program you can put an image into and draw a spline around the image should do. You'll need to export the spline as a Vue readable file though(3ds, obj etc.) I use Illustrator because its easier - you could probably use Freehand or any vector based program that allows you to draw a vector outline and save it as something like a dxf or whatever. PS I don't think you have to outline the gaps in the middle (I've never needed to) of the trees or anything - just the top, bottom, left and right extents of the image. The rest should be okay.