Also make sure you have all of the files you'r using in one folder. Gani Editor doesn't magicly sweep trough your computer and know that test.png is located in C
Documents and Settings\User\My Documents\Graal\My 1337 Graphics\
Make sure both the gani file and the graphic are in the same folder and also if you make any file changes to the png, reload the Gani Editor.
PS, there are enough tutorials to get you started, Blonkt's tutorial and even Chicken's recent tutorial are enough to teach you how to make a gani. (There is notting hard about it, I also suggest you try to refrain youself from making gani request since they will lead to seriously flaming!)