This is odd. I can't get the box centered over the sprite I want to grab. Can someone help?
grabbing
You have to edit the original image so that the tile you want to select will be in line with the preset grid.
That is, open up the image (in MS Paint) and move it until the selection box will line up with the tile/tiles you want (in ZQuest). It'll take some trial-and-error, unfortunately.