You need a tiling filter.

Try free  Simple Filters here:

http://www.btinternet.com/~cateran/simple/

Here is a tutorial on how to use it:

http://graphicssoft.about.com/library/weekly/aa080499p3.htm

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi