This might help:
1. In photoshop, make a new image with 500x500 dimensions (doesn't have to be that much, just big enough to fit every frame within it).
2. Fill the layer with a color.
3. Open each frame from your animation and place them wherever within the canvas you made manually using the move tool. You can undock the tab with the frame of animation and then drag the image into the new image you made.
4. Select the first layer you made, hold ctrl and then select the first frame of animation and go to Layer > Align > Vertical Centers. Do the same for Horizontal Centers.
5. Repeat step 4 with every frame.
EDIT: forgot that you have to go to Window > Animation and in the window that pops up, select the drop-down arrow and click "Make Frames From Layers" and then click the arrow again and select "Reverse Frames" this will create an animation out of your layers, but you select "Reverse Frames" because photoshop loads each frame in backwards. Also, this animation tool might not work with your PS, I use cs4 and 5 which both work.
This won't work perfectly, but it helps if you want to place things manually.
You can then select and area to crop and then choose "Save for web & Devices" to save as a gif.