Okay, first things first... a circle has no surface. If you're using the NURBS circle primative, the first you have to is use it to create a surface.
Select the circle primative then, from the surfaces menu select planar. Now select the newly created surface, right-click (and hold) on it to bring up the marking menu. From the bottom of the marking menu select Materials-->Assign new material-->(Shader type; blinn, lambert, etc.). The attribute editor for you new shader should open on the right of your screen. Left-click on the checkered option box to right of the color slider. This opens the create render node dialog. From this dialog select file. The attribute editor will shift to file options. Left-click on the folder icon and navigate to your .gif image. With the .gif selected, click the open button and your .gif should now be assigned to your surface. Be sure you're in the texture shaded view (press "6") or lighted view (press "7") in order to view the image on your surface. Animating is whole other area.
Good Luck and happy modelling.
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