Try downloading gimp. It's like photoshop, but free/open source. With a single button, you can offset the image, and blend it accross the edges, and it it makes it look flawless when tiled.
My install is 1.17Gb. it's open source, so you can get more packages (probably an infinite number), but out of the box it has an equivalent to all the photoshop addons. IMO, it's tiny. and it works fast and well.
