First Open up the image you want to use.
I choose this one.
2)
Select the Single Column Marquee Tool.
3)
Select the area that you want stretched.
4)
Go to EDIT > DEFINE PATTERN. Call it
anything your want.
5)
Now used the Rectangualr Marquee Tool select
the area to the right or left of the original
selection. I selected to the right.
6)
Go to EDIT > FILL. Select the patter
you created in step 4. Its usually the last
one. Also make sure the contents box is set
to pattern. Press OK and it should look like
this.
EXTRA: Or you can just get rid of the whole
picture and use the pixel stretch as the background
which sometimes looks better.