Altering skins & textures

MJW

I have managed to do a little modification of some skin textures, but this has led to further worries.
If I try to match the edges of a typical skin picture, the image when rendered does not work the same - there is a distinct line like a seam up the middle of the back. How do I prevent this? I assumed that matching the grid point at the 'edge' would do it - but no such luck...
Secondly,where can I find specific skin jpegs easily? I am currently trying to find the Teen Josie one, and frankly don't know how to find such things quickly and simply. There must be a way?!?!