I just did my first one with Picture Publisher 8. It has a fill tool and I selected an image to fill with and it tiled it. PP8 was available for $45 and while not a great paint prog and weak with layers, is very strong with web graphics and photo/image editing. Painter 6 looks to be very strong and has tools for producing seamless tiles, including the ability to paint off one side and have the brush come in on the other side of a tile in production..