Photoshop or Adobe ImageReady have features for creating animated GIFs. This should be a good way to get them properly formatted.
Here’s a quote from the Photoshop 7.0 help.
You can easily create animated GIFs from existing one-layer-per-frame images in Adobe Photoshop file format or from a group of single-layer images.
You can make each layer in a multilayer Photoshop file a separate frame in the Animation palette. The layers are placed in the Animation palette in their stacking order, with the bottom layer becoming the first frame.
You can also import a folder of files and use each file as a frame in ImageReady. Files can be in any format that ImageReady supports. Each file becomes a frame in the Animation palette. The files are placed in the Animation palette in alphabetical order by image filename.